The Adjutant General of Maryland is the head military official of the Maryland National Guard, the Maryland Defense Force, and any other military or paramilitary units that may be maintained by the State of Maryland. The adjutant general is responsible for the military department's budget and maintains all State-owned armories in Maryland.[1]
History
Maryland Governor Thomas Sim Lee provided for the office of an adjutant general of the State Militia in "an Act to regulate and discipline the militia of this State," in compliance with the Act of Congress of 1792, entitled, "An Act more effectually to provide for the national defence, by establishing a uniform militia throughout the United States."[2]
In October 1794, an adjutant general of Maryland was appointed for the first time and a resolution was passed at the November session of the Maryland General Assembly, as follows: "Resolved, That the treasurer of the Western Shore / be and he is hereby authorized and required to pay to The Adjutant-General of this State for the time being, the sum of two hundred pounds current money, in quarterly payments, provided the said Adjutant-General reside or keep an office at the seat of government."
In 1797, the annual salary of the office was "five hundred and thirty-three dollars and one-third of a dollar," six hundred dollars in 1799, and was later "fixed and established" by law, (chapter 168, Laws of Maryland. 1S07), at five hundred dollars annually, to be paid in quarter yearly payments. By subsequent enactments, the amount was increased at various times until the present salary was attained and established.
The Adjutant General of Maryland was given the relative military rank of "Colonel of Artillery in the line" by Chapter 251, Laws of Maryland, 1834; the relative rank of "Brigadier-General" by Chapter 284, Laws of Maryland, 1864; and finally, the present rank of "Major-General" by Chapter 337, Laws of Maryland, 1867.
List of Maryland Adjutant Generals
The following sketches have been adapted and borrowed from a variety of sources, including the Maryland State Archives and the Report of the Adjutant General of Maryland 1906–1907.[2]
Henry Carbery (1794–1807)
Henry Carbery, first adjutant general of Maryland, was born at St. Clement's Bay, St. Mary's county, Md., in 1757. At the commencement of the Revolutionary War in 1776, he was a "gentleman cadet" in Captain John Allen Thomas' "Independent" Company, of St. Mary's county and is mentioned in a letter from Captain Thomas to the Council of Safety, dated March 8, 1776, as "deserving notice." Carbery was appointed second lieutenant in Colonel Hartley's regiment of Continental Troops, January 24, 1777. He was promoted to first lieutenant on or about September 19, 1777, and captain on November 30, 1778. (The regiment was designated as the 11th Pennsylvania on January 13, 1779). He was wounded on August 13, 1779, and retired January 17, 1781. He was a captain in Major Henry Gaither's battalion of the "Levies of 1791," and he served under General St. Clair against the Miami Indians in November, 1791. Carbery became captain of infantry, U.S. Army, on March 16, 1792, and was assigned to the 4th sub-legion September 4, 1792. He resigned February 10, 1794.
Henry Carbery was appointed adjutant general of the Maryland State Militia October 6, 1794, and served under Governors Stone, Henry, Ogle, Mercer, Robert Bowie (1803) and Wright. He was made colonel of the 36th U.S. Infantry, March 22, 1813, and resigned March 4, 1815. He died at his residence, near Georgetown, D.C. on May 26, 1822, at 66 years old.
The following tribute to Maryland's first adjutant general, both as a soldier and as a man, was written by Hon. James Brice, of Annapolis, (president of the Governor's Council and acting governor upon the death of Governor Plater in 1792), in a communication to His Excellency, George Washington and is a copy of the original document:
Maryland Annapolis February 18th, 1792. In Council. Sir: Presuming that the defence of the frontiers will require an augmented force, and that Military promotions will of course take place, we beg leave to address you in favor of Mr. Henry Carbery, who served in the late expedition against the Indians as Senior Captain in the Battalion of levies from this State, and has returned with the reputation of having exhibited an exemplary conduct as well in the unfortunate action as during the Campaign in general. These testimonies joined to the knowledge we have of his respectable deportment in private life, have impressed us with the desire of procuring him the further notice of your Excellency. We believe him to be among those men who by a prediction for the Military life are led to a closer study of the duties of that profession than officers of his rank in general impose on themselves. We beg leave Sir, to add, that during the former war he occasionally commanded a party of Cavalry against the Indians, and seems confident of acquitting himself well if he should be honored with a Command of that kind in the proposed arrangements. With the highest respect we have the honor to be your excellency's Most Obedt. Hble. Servt. (Signed) James Brice His Excellency, the President of the United States.
Samuel Turbutt Wright (1807–1810)
Samuel T. Wright, second adjutant general of Maryland, was born in Queen Anne's county, Md., in the year 1749. He was chosen by the Convention of Maryland, 2 January 1776, second lieutenant of Captain Edward Veazey's Seventh "Independent" Company of Maryland Militia, enrolled from Queen Anne and Kent counties; taken prisoner at the battle of Long Island, 27 August 1776; later exchanged; commissioned captain, Second Maryland Regiment, 1 January 1777, (commanding Eighth Company of the Second Battalion); resigned 1 July 1779. Was appointed lieutenant-colonel, commandant, of the Thirty-eighth Regiment, (Queen Anne's county), Maryland Militia, 18 June 1794.
Samuel T. Wright was appointed adjutant general of the Maryland State Militia 18 July 1807, and was authorized by Governor Robert Wright, in July, 1807, to detach 5,863 men from the militia, as Maryland's quota of 100,000 men ordered by the President to be ready to take the field at a moment's notice, on account of the critical status of foreign relations at that time. He served under Governors Wright and Edward Lloyd. He was a member of the Governor's Council during the years 1781, 1782, 1785 and 1786; also, for some time held the office of Clerk of Queen Anne's county, Md.; was an original member of the Society of the Cincinnati. He died near Centreville, Md., 30 June 1810.
John Kilty (1810–1811)
John Kilty, third adjutant general of Maryland, was born in England in the year 1756 and was educated at St. Omer's College, in France. Was appointed by the Convention of Maryland, July, 1776, an ensign in Captain Edward Tillard's company of Anne Arundel county militia, in the 3rd Maryland battalion of the Flying Camp, vice John Gassaway, resigned; commissioned a second lieutenant in the 4th Maryland Regiment, 10 December 1776; promoted to first lieutenant 6 November 1777; served in Baylor's 3rd Regiment of Light Dragoons, Continental troops, as lieutenant to 1 February 1782, and as captain from that date to 10 November 1782, when the command was consolidated with the First Continental Dragoons; retained as captain, until 31 December 1782; was "deranged," 1 January 1783.
Was appointed captain of an Annapolis cavalry troop attached to the 8th Brigade, Anne Arundel County Light Dragoons, Maryland Militia, 18 June 1794; commissioned brigadier general, 8th brigade, 13 June 1810.
John Kilty was appointed adjutant general of Maryland, 7 July 1810, and served under Governor Edward Lloyd. He was a member of the Governor's Council from 1786 to 1793 and president thereof in 1790; was appointed by President Washington supervisor of the revenue of the United States in Maryland in June, 1795; was "register of the Land Office" in 1806; was an original member of the Society of the Cincinnati, being its secretary in 1784.
He died at his country seat near Annapolis, Md. on 27 May 1811.
John Gassaway (1811–1817)
John Gassaway, fourth adjutant general of Maryland, was born in Anne Arundel county, Md., 18 June 1754.
Was appointed by the convention of Maryland, 2 January 1776, a sergeant in Captain Nathaniel Ramsey's company, Colonel Smallwood's Maryland battalion; commissioned ensign in Captain Edward Tillard's company of Anne Arundel County militia in the 3rd Maryland battalion of the Flying Camp, July, 1776; second lieutenant in Smallwood's battalion, 10 December 1776; first lieutenant, 2nd Maryland regiment, 17 April 1777; promoted to be captain-lieutenant, 1 July 1779; captain in 2nd Maryland regiment, 2 April 1780; taken prisoner at Camden, 16 August 1780 and was prisoner on parole to the close of the war.
After the war, he held the captaincy of the "Volunteer Company of the city of Annapolis."
He was appointed a major in the 22nd Regiment, (Anne Arundel County), Maryland militia, 18 June 1794; commissioned lieutenant-colonel, commandant, 22nd regiment, 15 September 1795; also for a time, served as brigade inspector, 8th Brigade, Anne Arundel County militia; commissioned a captain in 22nd regiment, 22 March 1808; resigned.
John Gassaway was appointed adjutant general of Maryland, 6 June 1811, and served under Governors Edward Lloyd, Robert Bowie (1811), Winder and Ridgely, of Hampton.
He was register of wills for Anne Arundel County from 1787 to 1820 and was an original member of the Society of the Cincinnati.
He died in Annapolis, Md., 25 June 1820.
Richard Harwood, of Thomas (1817–1835)
Richard Harwood, of Thomas, fifth adjutant general of Maryland, was born in Anne Arundel County, Md., 7 March 1775.
Entered the Grammar School of St. John's College, Annapolis, 11 November 1789; entered St. John's College, 1 August 1792, and graduated with the degree of Bachelor of Arts, 13 November 1794.
Was commissioned lieutenant in Captain John Gwinn's company, 22nd regiment, Anne Arundel County, Maryland, militia, 23 October 1795; resigned, and was commissioned captain; promoted to be a major of the 22nd regiment, 30 July 1800; captain of a select company attached to 22nd regiment, 14 May 1802; re-commissioned major, 10 February 1804; lieutenant-colonel, commandant, 22nd Regiment, 10 March 1808.
Richard Harwood, of Thomas, was appointed adjutant general of Maryland, 30 January 1817, and served under Governors Ridgely, of Hampton, Goldsborough, Sprigg, Stevens, Kent, Daniel Martin (1828), T. K. Carroll, Daniel Martin (1830), Howard, and James Thomas.
He was one of the commissioners appointed in 1820, to supervise the erection of the present county Court House in Annapolis.
He died at Annapolis, Md., 4 April 1835.
John Nelson Watkins (1835–1856)
John N. Watkins, sixth adjutant general of Maryland, was born in Anne Arundel County, Md., 24 September 1790.
Was a member of the class of 1811, St. John's College, Annapolis, but does not appear to have graduated.
Entered the military service of the United States, War of 1812 (from 1812 to 1814), at Annapolis, in a volunteer company called the "United Guards," commanded successively, by Captains Samuel Maynard and Richard M. Chase, (in Colonel Zachariah Duvall's 22nd regiment, Anne Arundel county, Maryland militia); served as a corporal under Captain Maynard from 9 April to 29 May, and from 2 August to 31 August 1813; and as a private under Captain Chase from 9 July to 14 July, from 22 August to 23 September, and from 26 October to 2 November 1814, and was honorably discharged.
Commissioned ensign in Captain Thomas Franklin's company, 22nd regiment, Maryland militia, 8 August 1823; promoted to brigade inspector, 8th brigade, 1st division, Maryland militia, 29 September 1825; division inspector, 1st division, 15 May 1834.
John N. Watkins was appointed adjutant general of Maryland. 19 May 1835, with the rank of a "Colonel of Artillery in the line", (Chapter 251, Laws of Md., 1834), and served under Governors J. Thomas, Veasey, Grason, F. Thomas, Pratt, P. F. Thomas, Lowe and Ligon.
He was elected a delegate from Annapolis to the Legislature in October, 1827; was clerk of the Senate of Maryland and a member of the Board of Visitors and Governors of St. John's College.
He died in Baltimore, at an advanced age.
John Wilmot (1856–1858)
John Wilmot, seventh adjutant general of Maryland, was born at Annapolis, Md., in 1778.
Entered the Grammar School of St. John's College, Annapolis, 17 May 1790; was a member of the class of 1798, but does not appear to have graduated; after attaining to manhood, he removed to the city of Baltimore. Was commissioned ensign in Captain James Cheston's company, 5th regiment, Maryland militia, (Baltimore), 29 July 1809; ensign in Captain David Warfield's company, attached to same regiment, 29 July 1811; mustered in with his company, known as the "Baltimore United Volunteers," in the service of the United States during the War of 1812, retaining his rank of ensign; participated in the engagement at Bladensburg, 24 August 1814; was also present at the battle of North Point, 12 September 1814, in which action he had the command of his company and received special mention for conspicuous bravery during the battle, in Brigadier-General Strieker's report, of 15 September 1814, to Major General Samuel Smith, as follows: "Ensign Wilmot, commanding the company of United Volunteers of the 5th, and many of his men distinguished themselves;" was promoted to lieutenant of the company, (then under command of Captain William Cooke, Jr.,) 8 November 1814; was in the service of the United States from 19 August to 18 November 1814, when discharged.
Was commissioned captain, 5th regiment, infantry, Maryland militia, 10 November 1818; resigned.
Afterward engaged in mercantile life for several years in Baltimore, returning finally to Annapolis.
John Wilmot was appointed adjutant general of Maryland, with the rank of Colonel of Artillery, 10 March 1850, and served under Governors Ligon and Hicks. He was judge of the Orphans' Court of Anne Arundel County and held successively various public offices.
He died at Annapolis, Md., 4 March 1858. The funeral obsequies were conducted in the House of Delegates, in the old State House, and were attended by his Excellency the Governor, the state officials and the members of the General Assembly, then in session. By order of the Governor, the national flag was displayed at half-mast, and with solemn and impressive ceremonies the mortal remains of Colonel John Wilmot, seventh adjutant general of Maryland, were consigned to their final resting place.
Nicholas Brewer, of John (1858–1864)

Nicholas Brewer, of John, eighth adjutant general of Maryland, was born at Annapolis, Md., 24 October 1808.
Entered St. John's College, Annapolis, in 1825, and left in 1826; studied law and was admitted to the bar.
He was state's attorney for Anne Arundel County for a number of years, and does not appear to have performed any military service.
Nicholas Brewer, of John, was appointed adjutant general of Maryland, with the rank of Colonel of Artillery, 24 March 1858, and resigned 4 February 1864. He served under Governors Hicks and Bradford.
He was adjutant general during the Civil War (1861–1865), but beyond equipping and reviewing the troops sent to the front he had no military functions to perform.
He died at Annapolis, Md., 14 March 1874.
John Summmerfield Berry (1864–1869)
John S. Berry, ninth adjutant general of Maryland, was born in Baltimore, Md., 18 June 1822.
Was educated partly in Baltimore and partly at Dickinson College, Carlisle, Pa.; on leaving college, he entered upon a business career in Baltimore, becoming a successful merchant and, later, a manufacturer.
Was elected in 1857, a delegate to the Maryland Legislature from Baltimore County, Md., and was chosen speaker of the house in January, 1858; was again a member of the Legislature in 1861 and speaker of the house during the session of 1862.
Was an aide to Governor Hicks in 1857, and to Governor Bradford in 1861; a member of the Constitutional Convention of 1864.
John S. Berry was appointed adjutant general of Maryland, 10 February 1864, with the rank of brigadier general (Chapter 284, Laws of Maryland, 1864), and called out the Baltimore militia for the defense of the city, on the approach of the Confederates in July of that year; was re-appointed adjutant general, 24 March 1867, with the rank of major general, (Chapter 337, Laws of Maryland, 1867); he served under Governors Bradford, Swann and Oden Bowie, devoting much time to carrying out in all its particulars the law creating the "Maryland National Guard."
Was appointed, in 1885, a member of the Park Board of Baltimore, served for several years and discharged faithfully and diligently the duties of the position.
He died in Baltimore, 3 January 1901.
George Henry Bier (1869–1871)
George H. Bier, tenth adjutant general of Maryland, was born in Baltimore, Md., 11 July 1824.
Entered the Naval Academy as midshipman, 19 October 1841; warranted a passed midshipman from 10 August 1847; warranted as a master from 14 September 1855; promoted to lieutenant, 15 September 1855; ordered to the U.S.S. "Atalanta," for the Paraguay Expedition, in October, 1858; resigned from the U.S. Navy, to take effect from 23 April 1861.
Appointed first lieutenant, C.S. Navy,13 November 1861; appointed Major, C.S. Army, (with temporary rank), 14 July 1862, and ordered to report to General T. J. Jackson, serving as Chief of Ordnance; relieved from further duty as Major and Chief of Ordnance with General T. J. Jackson, 12 January 1863, and ordered to report to the Secretary of the C.S. Navy, at Richmond; participated in the attack of Confederate ironclads upon the Federal blockading fleet, on board the C.S.S. "Chicora", (Commander John R. Tucker, C.S.N., commanding), off Charleston, S. C, 31 January, 186.3; resigned from C.S. Navy, 25 June 1863; in February, 1864, was in command of the blockade-runner "Dee", and on 10 May 1864, was captured, while in command of the "Anglo-rebel blockade-runner Greyhound"; at the close of the war, returned to Baltimore.
George H. Bier was appointed adjutant general of Maryland, with rank of Major General, 6 April 1869, and served under Governor Oden Bowie; resigned 3 February 1871.
He died at Key West, Fla., 13 April 1905.
Charles Henry McBlair (1871–1874)
Charles H. McBlair, eleventh adjutant general of Maryland, was born in Baltimore, Md., 24 December 1809.
Entered the U.S. Navy as a midshipman, 4 March 1823; passed midshipman, 23 November 1829; commissioned a lieutenant from 12 July 1831, and ordered for duty as sailing master on the U.S.S. "Ontario" in the Mediterranean; returning to the United States, was ordered, successively, to the U.S.S. "Warren", to the Mediterranean Station, to the U.S.S. "Mississippi", and in October, 1842, to command the U.S.S. "Poinsett."
He served in the Mexican War (1846–1847), and commanded the bomb-barge "Stromboli;" detached from command of the "Stromboli," 2 September 1848.
Ordered to the Coast Survey during 1849, 1850–1852; transferred to command of the steamer "Walker", 15 July 1852; ordered to duty as light house inspector, 14 December 1852; promoted to commander, 18 April 1855, and ordered to command the steamer "Michigan", on the lakes, in September of that year; in January, 1861, was member of the naval examining board at Annapolis; resigned from the U.S. Navy, to take effect from 22 April 1861.
Was appointed from Maryland as commander, Confederate States Navy, 19 October 1861; was transferred temporarily to Army service, as captain and chief of artillery, and officer in charge of batteries at Fernandina, Fla., in December. 1861; appointed to temporary rank of colonel, to report to General Trapier, 13 January 1862; was on duty as colonel and chief of artillery. Department of Middle and East Florida, from December, 1861, to March, 1862; served on the C.S.S. "Capitol," in the Mississippi river, May, 1862; commanding C.S.S. "Morgan," September, 1862; appointed again commander, 23 October 1862, to rank from 26 March 1861; was in command at Mobile Bay, 1862–1863; commanding C.S.S. "Gaines", December, 1863; commanding C.S.S. "Tuscaloosa", 1863–1864 and C.S.S. "Huntsville", Mobile Bay, April, 1864; surrendered with General Joseph E. Johnson, at Greensboro, N.C.; was paroled, 28 April 1865, and returned to his home, "Bonnie Brae", Baltimore County, Md.
Commissioned colonel and aide-de-camp, on staff of Governor Oden Bowie, 20 April 1869; was appointed colonel and assistant adjutant general by Governor Bowie.
Charles H. McBlair was appointed adjutant general of Maryland, with the rank of major general, 8 February 1871, and was re-appointed 5 February 1872, serving under Governors Oden Bowie, Whyte, and Groome, (pro tem).
He died in Washington, D. C., 15 November 1890.
Frank A. Bond (1874–1880)
Frank A. Bond, twelfth adjutant general of Maryland, was born at Bel Air, Harford County, Md., in 1838, and moved to Jessups, Anne Arundel County, Md., in 1857.
In 1859, he raised a company of infantry, called the "United Rifles," and was commissioned captain by Governor Hicks; the company was disbanded and partially disarmed by U.S. troops in 1861, but the majority of the arms went south with Captain Bond, who was given the rank of captain by Governor Letcher of Virginia and was assigned, by written order of Colonel "Stonewall" Jackson, as drill-master, 8th Virginia infantry; enlisted as corporal, company M, 1st Virginia Cavalry, C.S. Army, 14 May 1861; elected second lieutenant, company M, 1 August 1861, and was afterwards dropped at the re-organization of the company, 5 May 1862.
In May, 1862, was instrumental in raising a company of cavalry that became company A, 1st Maryland Cavalry, C.S.A., and was elected first lieutenant; upon organization of the battalion, promoted to captain, company A, 12 November 1862; at Greenland Gap, W.V., 25 April 1863, all the senior officers were disabled, and Captain Bond commanded the battalion during the remainder of the campaign; company A was detailed for special duty in the Gettysburg campaign and Captain Bond was Provost Marshall during the three days they occupied the town; on 6 July 1863, Captain Bond's command was engaged in a brilliant action with a force under Colonel Ulric Dalghren at Hagerstown, Md., in which Bond was severely wounded and left a prisoner; was confined at Fort McHenry and at Point Lookout, but was exchanged in May, 1864; placed on the retired list of the regular C.S. Army, but in October, of the same year, accepted the position of adjutant general, with the rank of major, on the staff of General Leaventhorpe, commanding North Carolina troops; served until the close of the war and was paroled at Greensboro, N.C., 1 May 1865.
Returning to his home, at Jessups, Md., he raised a company of cavalry and was commissioned captain. This company became company G, 3rd Maryland Cavalry, and upon the organization of the 3rd Battalion of Cavalry, he was elected colonel and commissioned by Governor Oden Bowie, 22 November 1867; made brevet brigadier general 17 May 1869; brigadier general 2nd brigade, 3rd division, 25 May 1869; major general 14 May 1870, commanding 3rd Division, Maryland National Guard, until the expiration of their service.
Frank A. Bond was appointed adjutant general of Maryland, with the rank of major general, 4 April 1874; reappointed, 22 March 1876; served under Governors Groome, Carroll, and Hamilton, (pro tem).
John Wesley Watkins (1880–1884)
J. Wesley Watkins, thirteenth adjutant general of Maryland, was born in Baltimore, Md., in October, 1807.
Lived for seven years of his boyhood at West River, Anne Arundel County, and then removed to his native city; became a contractor and builder, and erected several of Baltimore's public edifices.
Was active in the state militia, serving from the ranks up; was commissioned second lieutenant in Captain Charles Howard's "Mechanical Volunteers", 5th regiment infantry, Maryland militia, 20 January 1836; promoted to first lieutenant, 25 May 1836; captain of the "Mechanical Volunteers" company, 21 May 1839; commissioned lieutenant colonel, 39th regiment infantry of Baltimore 3d June, 1846.
During the Mexican War (1846–1847), he was enrolled 10 June 1847, and mustered into the service of the United States, 24 July 1847, as captain of a company bearing his name, but no record of his service is found.
Was commissioned major, in the 5th regiment, infantry, attached to 1st Light Brigade, Maryland Volunteers of Baltimore 7 September 1847; appointed colonel 5th regiment, Maryland Volunteer Infantry, 5 February 1856; appointed brigadier general, 1st Light Brigade (composed of the 1st Light Cavalry regiment, a regiment of artillery and the Fifth Regiment), 14 February 1861, but not confirmed; no record of service in the Civil War (1861–1865).
Was a member of the Baltimore City Council as far back as 1837 and served several terms; was United States marshal under President Pierce's administration; chief engineer of the Baltimore Fire Department from 15 March 1868, to 15 June 1871, and held other public offices.
J. Wesley Watkins was appointed adjutant general of Maryland, with the rank of major general, 6 April 1880, and served under Governors Hamilton and McLane, (pro tem).
He died near Watersville, Carroll County, Md., 17 September 1887.
James Howard (1884–1892)
James Howard, fourteenth adjutant general of Maryland, was born in Baltimore, Md., 23 October 1832.
Educated at the private school of Mr. McNally in that city; entered service of U.S. Army.
Commissioned second lieutenant, company B, 3rd U.S. Artillery, 27 February 1857; served at Fort Columbus, New York Harbor, until December, 1857, and was then ordered to join his company at Benicia, Ca.; thence ordered to Fort Umpqua, Oregon Territory; in spring of 1858 was transferred with his company to Fort Vancouver, Washington Territory and on breaking out of hostilities with the Northern Indians was detailed with his company, along with several other commands, for duty with Colonel George Wright in his campaign against these tribes.
Returning in the Fall, was one of the escort of 100 men of 3rd artillery, to the expedition of Captain John Mullan, charged with the duty of constructing a military wagon road from Walla Walla to Fort Benton on the Upper Missouri river; returning from this expedition in the fall of 1860; was granted leave of absence for six months; resigned his commission 3 April 1861.
Entered the service of the C.S. Army at Montgomery, Ala. and was appointed first lieutenant of artillery, C.S. Army, 13 April 1861, to rank from 16 March 1861; ordered to report to General Braxton Bragg, at Pensacola, Fla., as Instructor of Artillery; appointed to temporary rank of lieutenant-colonel, to rank from 30 August 1862; served as aide-de-camp to Major General G. W. Smith, and also as lieutenant-colonel commanding heavy artillery in Richmond defenses; relieved from duty at Richmond, temporarily, and continued in command of the 18th and 20th battalions, Virginia Artillery, in the field.
On the retreat from Richmond, with the division of General G. W. Custis Lee, was engaged and captured in the battle of Sailor's Creek, two days before the surrender at Appomattox, and sent to Johnson's Island, whence he was liberated, after imprisonment of about six weeks, and returned to Baltimore.
Was commissioned colonel and aide-de-camp on the staff of Governor Oden Bowie, 8 February 1871; acting assistant adjutant general on the staff of Governor Whyte, 5 February 1872; was brigadier general and chief of artillery on the staff of Governor Whyte, in 1873; made brigadier general and chief of artillery on the staff of Governor Groome, 6 April 1874; resigned 4 June 1874.
Commissioned colonel of the 7th regiment, M.N.G., 24 July 1877, during the railroad riots of that year, and served until the regiment was disbanded, 23 August 1877.
James Howard was appointed adjutant general of Maryland, with the rank of major general, 8 April 1884; reappointed, 25 February 1886; again re-appointed, 21 February 1888; served under Governors McLane, Henry Lloyd and Jackson.
Henry Kyd Douglas (1892–1896)

Henry Kyd Douglas, fifteenth adjutant general of Maryland, was born at Sheperdstown, Va., (now West Virginia), 29 September 1840.
Graduated from Franklin-Marshall College in 1859; studied law, graduating in 1860.
Enlisted at Harper's Ferry as private, company B, 2nd Virginia infantry, ("Stonewall" Brigade), C.S. Army, 18 April 1861; promoted to be first sergeant, 5 June 1861; second lieutenant, 14 September 1861; appointed captain in 1862; major and assistant adjutant general to rank from 13 June 1863; was adjutant and inspector general of the "Stonewall" Brigade, from which he was transferred to a post as aide-de-camp on General "Stonewall" Jackson's staff; after Jackson's death served in succession on the staffs of Generals Edward Johnson. John B. Gordon, Jubal A. Early and others, commanding the "Stonewall" division and Jackson's corps; made colonel of the 13th and 14th Virginia regiments consolidated and assigned to command of the light brigade formerly commanded by Generals Early and A. P. Hill; was promoted to rank of brigadier general, but his commission did not reach him.
Was wounded severely at Gettysburg and for a short while confined in the old Capitol prison; was at Appomattox and was paroled 9 April 1865.
After the war he practiced law in Winchester, Va., and in 1868 came to Hagerstown, Md.
Was appointed Colonel and aide-de-camp on the staff of Governor Carroll, February, 1876; in 1877, during the railroad strikes of that year, in command of the Department of Western Maryland.
Captain, Hagerstown Light Infantry, 22 November 1880; commissioned lieutenant-colonel, 1st Battalion, Maryland Infantry, 29 September 1881; colonel, 1st Regiment, Maryland Infantry, (1st brigade), 29 May 1886; resigned, 16 April 1891.
Henry Kyd Douglas was appointed adjutant general of Maryland, with the rank of major general, 3 March 1892, and served under Governor Brown.
He died at Hagerstown, Md., 18 December 1903.
Lemuel Allison Wilmer (1896–1900)
L. Allison Wilmer, sixteenth adjutant general of Maryland, was born in Charles County, Md., 17 September 1849.
Educated in the public schools of Charles County and at Charlotte Hall Academy, St. Mary's County; for a time taught a public school in his native county. Entered the "Freshmen" class, St. John's College, Annapolis, 16 September 1867, graduating 26 July 1871, "first honor" man in his class; entered the Law School of the University of Maryland, Baltimore, in October, 1872, graduating 2 June 1874, and opened a law office in Baltimore that year, with the late John S. Wirt, Esq.; after practicing for seven years in that city, he returned to Charles county where he continued to practice his profession.
Enlisted in company "A," 5th regiment, M.N.G., as a private in 1877; commissioned second lieutenant, same company, 14 January 1879; captain, company "I," 5th regiment, 2 April 1880; resigned, 10 January 1882; elected captain of the "Howard Rifles," of Charles county and commissioned 7 September 1886; (the company was afterwards attached to the 1st regiment, M.N.G., and was known as company "E"); commissioned lieutenant-colonel, 1st regiment, infantry, 19 December 1888; promoted to colonel, 11 May 1891.
L. Allison Wilmer was appointed adjutant general of Maryland, with the rank of major general, 19 February 1896, and served under Governor Lowndes. He was elected state's attorney for Charles county in 1883, and re-elected in 1887; was again elected state's attorney in 1899 and re-elected in 1903 for four years and was president of the State Bar Association. General Wilmer lived in La Plata, Md.
John S. Saunders (1900–1904)
John S. Saunders, seventeenth adjutant general of Maryland, was born at Norfolk, Va., 30 January 1836.
Was educated, partly, in Norfolk and, partly at St. James' College, Hagerstown, Md.
When eighteen years old was appointed, by President Pierce, a cadet-at-large to West Point; was cadet at the U.S. Military Academy from 1 July 1854 to 1 July 1858, graduating with honors, the fifth in his class; was appointed brevet second lieutenant, 2nd artillery, U.S. Army, and assigned to duty as adjutant of the Battalion at West Point; transferred to Ordnance Department of the Army, 1 September 1858; (upon the occasion of the Prince of Wales' visit to this country in 1860, was aide to the Prince during his tour of the United States); appointed second lieutenant. 1 February 1861; resigned from the U.S. Army, 22 April 1861.
Was appointed first lieutenant, C.S. Artillery, 18 May 1861, to rank from 16 March 1861; promoted to captain of artillery, Provisional Army of Virginia, 8 May 1862; appointed to temporary rank of lieutenant-colonel, 14 November 1862, to report to General G. W. Smith; afterwards, served as lieutenant-colonel of artillery and chief-of ordnance; commanded six batteries of artillery in the successful attack upon Norfolk.
After General McClelland's retreat, was ordered to report to General Pemberton at Vicksburg, and was in charge of the fortifications in the siege of Vicksburg; was there captured, but promptly exchanged; assigned to duty as chief of artillery in the Inspector General's office, Department of the South—later, transferred to the Army of Northern Virginia; was detailed on special duty by President Davis; upon the evacuation of Richmond, rejoined the Army of Northern Virginia, surrendering at Appomattox; paroled, 9 April 1865.
He returned to Norfolk, but removed to Baltimore in 1867; entered the service of the Maryland National Guard as colonel and brigade inspector, 7 May 1887, and resigned, 7 February 1900.
John S. Saunders was appointed adjutant general of Maryland, with the rank of major general, 7 February 1900, and served under Governor Smith.
He died at Annapolis, Md., 19 January 1904. The body of Adjutant General Saunders was brought to Baltimore, and the public solemnities were conducted in the Fifth Regiment Armory, whence the funeral escort, consisting of one battalion from each of the several infantry regiments together with the cavalry troop of the Maryland National Guard, conveyed the body of the deceased to Greenmount Cemetery where it was interred with military honors.
Clinton Levering Riggs (1904–1908)
Clinton L. Riggs, eighteenth adjutant general of Maryland, was born in New York City, 13 September 1866; during the same year, his parents removed to Baltimore, Md.
At the age of eleven, he entered St. Paul's School, Concord, N. H.; later, entered Princeton University, and graduated, as civil engineer in 1887, standing second in his class.
After practicing his profession a short time in Iowa, returned to Baltimore and entered the machine shop of Robert Poole & Son Company; engaged with the Detrick and Harvey Machine Company, of Baltimore, 9 February 1891, and retired from business, as vice-president of that company, 15 January 1903.
Entered the service of the Maryland National Guard, as second lieutenant, Company E, 5th Regiment Infantry, 29 April 1890; elected captain, Company F, 5th regiment, 23 February 1891; commissioned major, 5th regiment, 12 November 1895; was mustered into the service of the United States, during the Spanish–American War, as major, 5th Maryland, U.S. Volunteer Infantry, 14 May 1898; mustered out with his regiment at the close of the war, 22nd, October, 1898; resigned from the Maryland National Guard, 26 January 1899.
Clinton L. Riggs, was appointed adjutant general of Maryland, with the rank of major general, 29 January 1904, and served under Governor Warfield.
Henry M. Warfield (1908–1912, 1916–1920)
Henry M. Warfield was born in Baltimore July 1, 1867. He was a son of the late Henry M. Warfield, who was a member of the State Legislature of 1861 and the candidate for mayor of Baltimore on the reform ticket in 1875.
General Warfield's connection with the National Guard of Maryland dates from November 1, 1885, when he enlisted as a private in Company K, 5th Infantry, serving as such until November 1, 1888, the date of his election as second lieutenant of that company. He was elected first lieutenant Company F, 5th Infantry, April 16, 1891, serving in this position until commissioned captain and inspector of rifle practice on the Regimental Staff, March 14, 1892. He was elected captain Company B, 5th Infantry, December 12, 1892, and major, 5th Infantry, October 28, 1895. He served as a major in this regiment until June 30, 1903, on which date he was elected and commissioned colonel of the Regiment, holding this position until appointed adjutant general by His Excellency Governor Crothers, January 22, 1908.
General Warfield was again appointed adjutant general by Governor Harrington March 3, 1916.
During the Spanish–American War, he was mustered into the service of the United States as major in the 5th Maryland, U. S. Volunteer Infantry, May 13, 1898, serving until this regiment was mustered out, October 22, 1898.
General Warfield always took much interest in the affairs of his native city, both business and social. He was the resident manager of the Royal Insurance Company, Ltd., of Liverpool, with offices in the Chamber of Commerce Building, Baltimore, and one of the directors of the Board of Trade, and Farmers' and Merchants' Bank, Baltimore. His membership in the clubs of Baltimore includes the Maryland, Elkridge, Merchants' and Bachelors' Cotillon.
Charles F. Macklin (1912–1916)

Charles F. Macklin was born in Ft. Sully, S.D. on April 21, 1871, and later moved to Ilchester, Md.
Macklin was educated in public schools and DeVeaugh College, Suspension Bridge, N.Y. He was a midshipman at the U.S. Naval Academy in Annapolis from 1888–1892 and served at sea from 1892 through 1894.
Macklin was commissioned as a second lieutenant U.S. Marine Corps July 1, 1894, and resigned July 1, 1896. He joined the Maryland National Guard (1st Brigade) Feb. 11, 1901 and served as inspector general. Macklin became commander of the 4th Maryland Infantry Aug. 19, 1904. He was promoted to brigadier general and commander of the Maryland National Guard's 1st Brigade on Nov. 17, 1909.
Macklin was a key member of the 4th Maryland Infantry and was a driving force behind the emphasis on rifle marksmanship in the MDNG in the early 20th Century. He himself was one of the captains of a Maryland rifle team that won several competitions.
Macklin was assigned as adjutant general of Maryland on Feb. 2, 1912 and retired March 4, 1916. He then assumed command of the Maryland Naval Militia (then part of the Maryland National Guard) on April 12, 1916. He died in Baltimore on April 16, 1945.
Milton A. Reckord (1920–1941, 1945–1965)

Milton Atchison Reckord (December 28, 1879 – September 8, 1975) was an important figure in the history of the National Guard of the United States. Reckord expressed desire to serve in the military, but at the request of his mother, delayed entry into service until he turned 21. He enlisted in Company D, 1st Maryland Infantry, Maryland National Guard on February 15, 1901, and would eventually rise to command the same company when he was commissioned as a captain in December 1904. As a major, in 1916, Reckord was given command of the 2nd Battalion, 1st Maryland Infantry, which deployed to the Mexican border and served in the Mexican Expedition commanded by Gen. John J. Pershing. When the 29th Infantry Division was created on the eve of World War I in 1917, Reckord was given command of one of its regiments, the 115th Infantry, which saw combat during the Meuse-Argonne Offensive.
In 1920, he was appointed adjutant general of the Maryland National Guard and, in 1934, while still serving as Maryland's adjutant general, he assumed command of the 29th Infantry Division.
During the years between the First and Second World War, Reckord was a leading advocate for increasing the role of the National Guard in the United States' national defensive strategy. From 1923 to 1925, he served as president of the National Guard Association of the United States. In 1933, he authored legislation that permanently gave National Guard personnel status as both state and federal troops.
Reckord was mobilized for World War II with the 29th Infantry Division in February 1941 and took a leave of absence from his post as Maryland's adjutant general. Deemed by the Army to be too old to command a division in combat, he was relieved of command and assigned as the commander of the III Corps Area. He later deployed overseas and was named Theater Provost Marshal, European Theater of Operations.
After World War II, Reckord returned to his post as the adjutant general of Maryland. He was promoted to Lieutenant General by Governor J. Millard Tawes in 1961, and continued to serve as adjutant general until his retirement in 1966.
Reckord was born to John and Lydia (Zimmerman) Reckord at their home in Harford County, Maryland. He commenced work at his father's milling plant in 1896 upon his graduation from Bel Air High School. He was married to Bessie Payne Roe from 1910 until her death in 1943, and had one daughter with her, Gladys Atchison Reckord.
Francis Petrott (1941–1945, acting)
Francis Petrott was born in New York City, April 6, 1896. He attended private and public schools of New York and Connecticut; Georgetown University, 1914–17, graduated 1921; Princeton University, School of Military Aeronautics, graduated 1921; Yale University Graduate School, 1921–25. Married Mary Catherine James of Frederick, Maryland, September 11, 1921; one daughter, Doris Ann.
Served in the U.S. Army, 1917–21; U.S. Officer Reserve Corp after 1921; promoted to brigadier general during World War II. Engaged in the private practice of law, Frederick, Maryland. Acting adjutant general and acting chief of staff, staff of Governor Harry W. Nice, 1935. Appointed Maryland secretary of state, 1939–41 by Governor Herbert R. O'Conor. Adjutant general, 1941–45. Member, Frederick County Bar Association. Attorney for the Maryland Industrial Finance Company; Frederick County Beer Dealers' Association. Commander of the Francis Scott Key Post American Legion. Commander of Washington and Lee Chapter, Disabled American Veterans of the World War. President, Frederick Kiwanis Club. Exalted Ruler of Frederick Lodge No. 684, B. P. O. Elks. First vice president of the State Elks Association. President, Catoctin Country Club. Member, Executive Committee, Frederick Cotillion Club.
George M. Gelston (1965–1970)

George M. Gelston's tenure as adjutant general of Maryland was an active one as the Maryland National Guard was called into state duty several times (and federalized once) in response to severe domestic disturbances in Maryland. Gelston was instrumental in defusing the Cambridge riot of 1963 and the Baltimore riot of 1968.
In World War II, Gelston served as a liaison pilot with an artillery unit in the European theater of operations. He joined the Maryland National Guard in 1947 as the 29th Division's chief artillery air officer. Later, he participated in the Maryland National Guard's air defense program in the Baltimore-Washington area, serving as commanding officer of the 684th Anti-aircraft Artillery Battalion (90mm gun).
He held the position of assistant adjutant general in 1966. The Maryland National Guard armory in White Oak was named in his honor.
Edwin Warfield III (1970–1979)

Born in Baltimore, June 3, 1924, son of Edwin Warfield, Jr. resided at the "Oakdale," Warfield family estate in Howard County. Attended Gilman School; graduated in 1942 from Kent School, Connecticut; attended Cornell University; The Johns Hopkins University; University of Maryland, B.S., Agriculture, 1950. Married Carol Horton in 1947; five children; Edwin Warfield IV, John W. Warfield, Elizabeth W., Diana W., Karen. Married Ellen "Niki" Owens in 1967. Died of congestive heart failure at St. Agnes Health-Care, October 4, 1999.
General Assembly House of Delegates, Howard County, 1963–70. Chair, Agriculture and Natural Resources Committee, 1963–70.
Private Career and Other Public Service; Enlisted in the Army Air Corps, 1943; served in the Pacific during World War II. Retired Commander, Maryland National Guard.
Adjutant general of Maryland, 1970–80. Chairman of the Board and Chief Executive of The Daily Record, founded by his grandfather Edwin Warfield, Governor of Maryland from 1904 to 1908. Chair, Governor's Commission on the Expansion of the University of Maryland. Member, Warfield Commission on higher education in Maryland; World War II Memorial Commission; Maryland Club, South River Club, Sons of the American Revolution, Howard County Hunt Club, Bachelors Cotillion. Communicant, St. Andrew Episcopal Church in Glenwood, Howard County, and St. John Episcopal Church, Ellicott City.
Warren D. Hodges (1980–1987)

Warren D. Hodges was born in Lawrence, Kan. and attended the University of Kansas, where he played baseball and football before joining the Army in 1942. He later earned a degree from the University of Nebraska. He was also a graduate of several military command schools.
Hodges served during World War II in France and Germany, where he was wounded, and was later assigned to Japan, where he was General Douglas MacArthur's honor guard commander.
In July 1950, he returned to active duty in Korea as a battalion commander and regimental operations officer. He then served in the United States, Greece and Pakistan. He was deputy chief of the National Guard at the Pentagon before going to Vietnam, where he served as a brigade commander and division chief of staff. In 1969, he became chief of staff at Aberdeen Proving Ground and then commander of the combined Edgewood Arsenal and APG. He retired in 1972. He became an assistant secretary for capital planning in the state Department of Planning, and was named to head the Maryland National Guard by Governor Harry R. Hughes in 1980. He held the post until 1987.
Among his awards were the Combat Infantryman Badge with two stars, Distinguished Service Medal, Silver Star, Legion of Merit, Bronze Star and Purple Heart. He belonged to many veterans and military societies.
James F. Fretterd (1987–2002)

James F. Fetterd served as the adjutant general of Maryland from February 1987 to January 15, 2003.[3]
Born in Staten Island, New York, November 2, 1930. U.S. Army Command and General Staff College, 1973; U.S. Army War College, 1977. University of the State of New York, B.S. (sociology), 1984; Senior Executives Programs in National and International Security, Harvard University, 1987. Two daughters.
Member, Governor's Commission on Maryland Military Monuments, 1989–2003; Task Force on Youth Citizenship and Violence Prevention, 1995–96; World War II Memorial Commission, 1997–98; Executive Committee, Maryland Terrorism Forum, 1998–2003; Governor's Year-2000 Readiness Task Force, 1999–2000; Governor's Executive Council, 1999–2003; Cabinet Council on Criminal and Juvenile Justice, 1999–2003; Maryland Security Council, 2002–03. Chair, General Officer Steering Committee on National Guard Participation in International Affairs, National Guard Bureau (includes oversight of State Partnership for Peace Program). chief of staff, Maryland Army National Guard, 1976–81. assistant adjutant general for Army, 1981–87.
Bruce F. Tuxill (2002–2008)

Major General Bruce F. Tuxill served as the adjutant general of Maryland from January 15, 2003, to June 1, 2008.[4]
Born in Geneva, New York, November 10, 1945. Salem College, B.S. (business administration), 1967. Graduate, Capstone Program, National Defense University, 1996; National Security College; Combined Force Air Component Commander Course, U.S. Air Force. Chair, Air Reserve Forces Policy Committee. Former chair, Air National Guard Council, Air Force Association. Former chair, Resolutions Committee (former chair, resolutions air subcommittee), National Guard Association of the United States. Defense Distinguished Service Medal, 2002.
Assistant adjutant general for Air, 1994–2000. Officer and pilot, Maryland National Guard, 1968–2000 (pilot training, 1968–69; squadron pilot, 104th Tactical Fighter Squadron, 1969–76; chief, standardization & evaluation, 175th Fighter Group, 1976–78; operations officer, 175th Fighter Group, 1978–80; squadron commander, 104th Fighter Squadron, 1980–82; deputy commander for operations, 175th Fighter Group, 1982–83; commander, 175th Fighter Group, 1983–94).
Air National Guard Assistant to Commander, U.S. Air Forces Europe (USAFE), April 2000 to January 2003.
Co-Chair, Executive Committee, Maryland Terrorism Forum, 2003. Member, Maryland Security Council, 2003–05; Governor's Executive Council, 2003–08; Homeland Security Senior Policy Group, 2004; Task Force to Study State Assistance to Veterans, 2006–08.
Member, Executive Committee, Anti-Terrorism Advisory Council of Maryland, U.S. Attorney's Office, 2003–08.
James A. Adkins (2008–2015)

Major General James A. Adkins served as the adjutant general of Maryland from June 1, 2008, to January 21, 2015.[5]
General Adkins was born in Cambridge and grew up in Dorchester County on Maryland's Eastern Shore. Prior to entering the U.S. Army, he served two years with the Dorchester County Sheriff's Office.[5]
His military career spans more than 30 years of service in both the enlisted and officer ranks. He has served at nearly every level of command and in various staff assignments. He is a graduate of the  Defense Language Institute's Russian Language Program in Monterey, Ca. and served in intelligence, infantry and cavalry assignments in the United States and abroad. His military assignments also included director of military support to civil authorities, counter-drug taskforce commander and coordinator of emergency management operations. After the collapse of the Soviet Union, he assisted the Republic of Estonia in its transition to democracy.
General Adkins' military decorations include the Legion of Merit, the Maryland Distinguished Service Cross and the Order of the White Cross from the Republic of Estonia.
General Adkins served in the Maryland Military Department as chief of staff and assistant adjutant general for state operations. He also served as director of the Cemetery and Memorial Programs and as the deputy secretary of Veterans Affairs. In May 2007, Governor Martin O'Malley appointed General Adkins to his cabinet as the secretary of Veterans Affairs. He served as the state's key advisor for veteran issues until September 2009. For more than a year and a half, General Adkins simultaneously held two cabinet-level positions in the O'Malley administration while serving as the adjutant general.
Linda L. Singh (2015-present)

Major General (MD) Linda L. Singh served as the acting adjutant general from January 21 to March 27, 2015, when she was then appointed as the 29th adjutant general of Maryland.[6]
Singh was born in Frederick, Maryland, and is a long time Maryland resident. She received her commission in 1991 through the Maryland Military Academy's Officer Candidate School in Reisterstown, Md.[6]
Her military career spans more than 30 years of service in both the enlisted and officer ranks. She has served at nearly every level of command and in various staff assignments two of which were oversea deployments to Kosovo and a combat tour to Afghanistan supporting Operation Enduring Freedom. Her previous military assignments include commander of the Maryland Army National Guard and Director of the Joint Staff.[6]

A History of the Adjutants General of Maryland

Who was the first Adjutant General of Maryland?


A Geiger counter is an instrument used for detecting and measuring ionizing radiation. Also known as a Geiger-Mueller counter (or Geiger-Müller counter), it is widely used in applications such as radiation dosimetry, radiological protection, experimental physics, and the nuclear industry.
It detects ionizing radiation such as alpha particles, beta particles, and gamma rays using the ionization effect produced in a Geiger–Müller tube, which gives its name to the instrument.[1] In wide and prominent use as a hand-held radiation survey instrument, it is perhaps one of the world's best-known radiation detection instruments.
The original detection principle was realized in 1908, at the Cavendish laboratory, but it was not until the development of the Geiger-Müller tube in 1928 that the Geiger counter could be produced as a practical instrument. Since then, it has been very popular due to its robust sensing element and relatively low cost. However, there are limitations in measuring high radiation rates and the energy of incident radiation.[2]
Principle of operation

A Geiger counter consists of a Geiger-Müller tube (the sensing element which detects the radiation) and the processing electronics, which displays the result.
The Geiger-Müller tube is filled with an inert gas such as helium, neon, or argon at low pressure, to which a high voltage is applied. The tube briefly conducts electrical charge when a particle or photon of incident radiation makes the gas conductive by ionization.  The ionization is considerably amplified within the tube by the Townsend discharge effect to produce an easily measured detection pulse, which is fed to the processing and display electronics. This large pulse from the tube makes the Geiger counter relatively cheap to manufacture, as the subsequent electronics are greatly simplified.[2]   The electronics also generate the high voltage, typically 400–900 volts, that has to be applied to the Geiger-Müller tube to enable its operation. To stop the discharge in the Geiger-Müller tube a little halogen gas or organic material (alcohol) is added to the gas mixture.
Readout
There are two types of detected radiation readout: counts or radiation dose. The counts display is the simplest and is the number of ionizing events detected displayed either as a count rate, such as "counts per minute" or "counts per second", or as a total number of counts over a set time period (an integrated total). The counts readout is normally used when alpha or beta particles are being detected. More complex to achieve is a display of radiation dose rate, displayed in a unit such as the sievert which is normally used for measuring gamma or X-ray dose rates. A Geiger-Müller tube can detect the presence of radiation, but not its energy, which influences the radiation's ionizing effect. Consequently, instruments measuring dose rate require the use of an energy compensated Geiger-Müller tube, so that the dose displayed relates to the counts detected.[2] The electronics will apply known factors to make this conversion, which is specific to each instrument and is determined by design and calibration.
The readout can be analog or digital, and modern instruments are offering serial communications with a host computer or network.
There is usually an option to produce audible clicks representing the number of ionization events detected. This is the distinctive sound normally associated with hand held or portable Geiger counters. The purpose of this is to allow the user to concentrate on manipulation of the instrument whilst retaining auditory feedback on the radiation rate.
Limitations
There are two main limitations of the Geiger counter. Because the output pulse from a Geiger-Müller tube is always of the same magnitude (regardless of the energy of the incident radiation), the tube cannot differentiate between radiation types.[2] Secondly, the inability to measure high radiation rates due to the "dead time" of the tube. This is an insensitive period after each ionization of the gas during which any further incident radiation will not result in a count, and the indicated rate is, therefore, lower than actual. Typically the dead time will reduce indicated count rates above about 104 to 105 counts per second depending on the characteristic of the tube being used.[2] While some counters have circuitry which can compensate for this, for accurate measurements ion chamber instruments are preferred for high radiation rates.
Types and applications

The intended detection application of a Geiger counter dictates the tube design used. Consequently, there are a great many designs, but they can be generally categorized as "end-window", windowless "thin-walled", "thick-walled", and sometimes hybrids of these types.
Particle detection
The first historical uses of the Geiger principle were for the detection of alpha and beta particles, and the instrument is still used for this purpose today. For alpha particles and low energy beta particles, the "end-window" type of a Geiger-Müller tube has to be used as these particles have a limited range and are easily stopped by a solid material. Therefore, the tube requires a window which is thin enough to allow as many as possible of these particles through to the fill gas. The window is usually made of mica with a density of about 1.5 - 2.0mg/cm2.[1]
Alpha particles have the shortest range, and to detect these the window should ideally be within 10mm of the radiation source due to alpha particle attenuation.[1] However, the Geiger-Müller tube produces a pulse output which is the same magnitude for all detected radiation, so a Geiger counter with an end window tube cannot distinguish between alpha and beta particles.[2] A skilled operator can use varying distance from a radiation source to differentiate between alpha and high energy beta particles.
The "pancake" Geiger-Muller tube is a variant of the end-window probe, but designed with a larger detection area to make checking quicker. However, the pressure of the atmosphere against the low pressure of the fill gas limits the window size due to the limited strength of the window membrane.
Some beta particles can also be detected by a thin-walled "windowless" Geiger-Müller tube, which has no end-window, but allows high energy beta particles to pass through the tube walls. Although the tube walls have a greater stopping power than a thin end-window, they still allow these more energetic particles to reach the fill gas.[1]
End-window Geiger counters are still used as a general purpose, portable, radioactive contamination measurement and detection instrument, owing to their relatively low cost, robustness and their relatively high detection efficiency; particularly with high energy beta particles.[2][3] However, for discrimination between alpha and beta particles or provision of particle energy information, scintillation counters or proportional counters should be used.[4] Those instrument types are manufactured with much larger detector areas, which means that checking for surface contamination is quicker than with a Geiger counter.
Gamma and X-ray detection
Geiger counters are widely used to detect gamma radiation and X-rays collectively known as photons, and for this the windowless tube is used. However, detection efficiency is low compared to alpha and beta particles.
The article on the Geiger-Muller tube carries a more detailed account of the techniques used to detect photon radiation. For high energy photons the tube relies on the interaction of the radiation with the tube wall, usually a high Z material such as chrome steel of 1–2mm thickness to produce electrons within the tube wall. These enter and ionize the fill gas.[2]
This is necessary as the low-pressure gas in the tube has little interaction with higher energy photons. However, as photon energies decrease to low levels there is greater gas interaction and the direct gas interaction increases. At very low energies (less than 25 KeV) direct gas ionisation dominates and a steel tube attenuates the incident photons. Consequently, at these energies, a typical tube design is a long tube with a thin wall which has a larger gas volume to give an increased chance direct interaction of a particle with the fill gas.[1]

Above these low energy levels, there is a considerable variance in response to different photon energies of the same intensity, and a steel-walled tube employs what is known as "energy compensation" in the form of filter rings around the naked tube which attempts to compensate for these variations over a large energy range.[1] A chrome steel G-M tube is about 1% efficient over a wide range of energies.[1]
Neutron detection

A variation of the Geiger tube is used to measure neutrons, where the gas used is boron trifluoride or helium-3 and a plastic moderator is used to slow the neutrons. This creates an alpha particle inside the detector and thus neutrons can be counted.
Gamma measurement—personnel protection and process control
The term "Geiger counter" is commonly used to mean a hand-held survey type meter, however the Geiger principle is in wide use in installed "area gamma" alarms for personnel protection, and in process measurement and interlock applications.
A Geiger tube is still the sensing device, but the processing electronics will have a higher degree of sophistication and reliability than that used in a hand held survey meter.
Physical design

For hand-held units there are two fundamental physical configurations: the "integral" unit with both detector and electronics in the same unit, and the "two-piece" design which has a separate detector probe and an electronics module connected by a short cable.
In the 1930s a mica window was added to the cylindrical design allowing low-penetration radiation to pass through with ease.[5]
The integral unit allows single-handed operation, so the operator can use the other hand for personal security in challenging monitoring positions, but the two piece design allows easier manipulation of the detector, and is commonly used for alpha and beta surface contamination monitoring where careful manipulation of the probe is required or the weight of the electronics module would make operation unwieldy. A number of different sized detectors are available to suit particular situations, such as placing the probe in small apertures or confined spaces.
Gamma and X-Ray detectors generally use an "integral" design so the Geiger–Müller tube is conveniently within the electronics enclosure. This can easily be achieved because the casing usually has little attenuation, and is employed in ambient gamma measurements where distance from the source of radiation is not a significant factor. However, to facilitate more localised measurements such as "surface dose", the position of the tube in the enclosure is sometimes indicated by targets on the enclosure so an accurate measurement can be made with the tube at the correct orientation and a known distance from the surface.
There is a particular type of gamma instrument known as a "hot spot" detector which has the detector tube on the end of a long pole or flexible conduit. These are used to measure  high radiation gamma locations whilst protecting the operator by means of distance shielding.
Particle detection of alpha and beta can be used in both integral and two-piece designs. A pancake probe (for alpha/beta) is generally used to increase the area of detection in two-piece instruments whilst being relatively light weight. In integral instruments using an end window tube there is a window in the body of the casing to prevent shielding of particles.  There are also hybrid instruments which have a separate probe for particle detection and a gamma detection tube within the electronics module. The detectors are switchable by the operator, depending the radiation type that is being measured.
Guidance on application use
In the United Kingdom the National Radiological Protection Board issued a user guidance note on selecting the best portable  instrument type for the radiation measurement application concerned.[4]. This covers all radiation protection instrument technologies and includes a guide to the use of G-M detectors.
History

In 1908 Hans Geiger, under the supervision of Ernest Rutherford at the Victoria University of Manchester (now the University of Manchester), developed an experimental technique for detecting alpha particles that would later be used to develop the Geiger-Müller tube in 1928.[6] This early counter was only capable of detecting alpha particles and was part of a larger experimental apparatus. The fundamental ionization mechanism used was discovered by John Sealy Townsend between 1897 and 1901,[7] and is known as the Townsend discharge, which is the ionization of molecules by ion impact.
It was not until 1928 that Geiger and Walther Müller (a PhD student of Geiger) developed the sealed Geiger-Müller tube which used basic ionization principles previously used experimentally. Small and rugged, not only could it detect alpha and beta radiation as prior models had done, but also gamma radiation.[5][8] Now a practical radiation instrument could be produced relatively cheaply, and so the Geiger counter was born. As the tube output required little electronic processing, a distinct advantage in the thermionic valve era due to minimal valve count and low power consumption, the instrument achieved great popularity as a portable radiation detector.
Modern versions of the Geiger counter use the halogen tube invented in 1947 by Sidney H. Liebson.[9] It superseded the earlier Geiger-Müller tube because of its much longer life and lower operating voltage, typically 400-900 volts.[10]
Gallery

Use of a "hot spot" detector on a long pole to survey waste casks.
G-M pancake detector feeding a microcontroller data-logger sending data to a PC via bluetooth. A radioactive rock was placed on top the G-M causing the graph to rise.
G-M counters being used as gamma survey monitors, seeking radioactive satellite debris

See also
Becquerel, the SI unit of the radioactive decay rate of a quantity of radioactive material
Civil Defense geiger counters, handheld radiation monitors, both G-M and ion chambers
Counting efficiency the ratio of radiation events reaching a detector and the number it counts
Dosimeter, a device used by personnel to measure what radiation dose they have received
Ionization chamber, the simplest ionising radiation detector
Gaseous ionization detectors, an overview of the main gaseous detector types
Geiger–Müller tube, provides a more detailed description of Geiger-Müller tube operation and types
Geiger plateau, the correct operating voltage range for a Geiger-Müller tube
Photon counting
Radioactive decay, the process by which unstable atoms emit radiation
Safecast (organization), use of Geiger-Müller counter technology in citizen science
Scintillation counter, a gasless radiation detector
Sievert, the SI unit of effects of low levels of radiation on the human body

 Media related to Geiger counters at Wikimedia Commons

How little amount of radiation can a geiger counter pick up?


Vertebrates /ˈvɜːrtɪbrɪts/ comprise all species of animals within the subphylum Vertebrata /-eɪ/ (chordates with backbones). Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,276 species described.[4] Vertebrates include the jawless fishes and jawed vertebrates, which include the cartilaginous fishes (sharks, rays, and ratfish) and the bony fishes.
Other vertebrates are the tetrapods, which include a bony fish clade known as the lobe-finned fishes, as well as amphibians, reptiles, birds and mammals.
Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7mm (0.30in), to the blue whale, at up to 33m (108ft). Vertebrates make up less than five percent of all described animal species; the rest are invertebrates, which lack vertebral columns.
The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution,[5] though their closest living relatives, the lampreys, do.[6] Hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as "Craniata" when discussing morphology.
Molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys,[7] and so also are vertebrates in a monophyletic sense. Others consider them a sister group of vertebrates in the common taxon of craniata.[8]
Etymology
The word origin of vertebrate derives from the Latin word vertebratus (Pliny), meaning joint of the spine.[9] The Proto-Indo-European language origins are still unclear.
Vertebrate is derived from the word vertebra, which refers to any of the bones or segments of the spinal column.[10]
Anatomy and morphology

All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal (vertebral column and/or notochord),[11] with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below.
In all vertebrates, the mouth is found at, or right below, the anterior end of the animal, while the anus opens to the exterior before the end of the body. The remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut.[12]
Vertebral column
The defining characteristic of a vertebrate is the vertebral column, in which the notochord (a stiff rod of uniform composition) found in all chordates has been replaced by a segmented series of stiffer elements (vertebrae) separated by mobile joints (intervertebral discs, derived embryonically and evolutionarily from the notochord).
However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon[13] and coelacanth. Jawed vertebrates are typified by paired appendages (fins or legs, which may be secondarily lost), but this trait is not required in order for an animal to be a vertebrate.

Gills

All basal vertebrates breathe with gills. The gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch.[14] The bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their chordate relatives have more than 50 pairs of gills.[12]
In amphibians and some primitive bony fishes, the larvae bear external gills, branching off from the gill arches.[15] These are reduced in adulthood, their function taken over by the gills proper in fishes and by lungs in most amphibians. Some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods.[16]
While the more derived vertebrates lack gills, the gill arches form during fetal development, and form the basis of essential structures such as jaws, the thyroid gland, the larynx, the columella (corresponding to the stapes in mammals) and, in mammals, the malleus and incus.[12]
Central nervous system
The central nervous system of vertebrates is based on a hollow nerve cord running along the length of the animal. Of particular importance and unique to vertebrates is the presence of neural crest cells. These are progenitors of stem cells, and critical to coordinating the functions of cellular components.[17] Neural crest cells migrate through the body from the nerve cord during development, and initiate the formation of neural ganglia and structures such as the jaws and skull.[18][19][20]
The vertebrates are the only chordate group to exhibit cephalisation, the concentration of brain functions in the head. A slight swelling of the anterior end of the nerve cord is found in the lancelet, a chordate, though it lacks the eyes and other complex sense organs comparable to those of vertebrates. Other chordates do not show any trends towards cephalisation.[12]
A peripheral nervous system branches out from the nerve cord to innervate the various systems. The front end of the nerve tube is expanded by a thickening of the walls and expansion of the central canal of spinal cord into three primary brain vesicles: The prosencephalon (forebrain), mesencephalon (midbrain) and rhombencephalon (hindbrain), further differentiated in the various vertebrate groups.[21] Two laterally placed eyes form around outgrowths from the midbrain, except in hagfish, though this may be a secondary loss.[22][23] The forebrain is well developed and subdivided in most tetrapods, while the midbrain dominates in many fish and some salamanders. Vesicles of the forebrain are usually paired, giving rise to hemispheres like the cerebral hemispheres in mammals.[21]
The resulting anatomy of the central nervous system, with a single hollow nerve cord topped by a series of (often paired) vesicles, is unique to vertebrates. All invertebrates with well-developed brains, such as insects, spiders and squids, have a ventral rather than dorsal system of ganglions, with a split brain stem running on each side of the mouth or gut.[12]
Evolutionary history

First vertebrates

Vertebrates originated about 525 million years ago during the Cambrian explosion, which saw the rise in organism diversity. The earliest known vertebrate is believed to be the Myllokunmingia.[1] Another early vertebrate is Haikouichthys ercaicunensis. Unlike the other fauna that dominated the Cambrian, these groups had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail.[24] All of these early vertebrates lacked jaws in the common sense and relied on filter feeding close to the seabed.[25] A vertebrate group of uncertain phylogeny, small-eel-like conodonts, are known from microfossils of their paired tooth segments from the late Cambrian to the end of the Triassic.[26]
From fish to amphibians

The first jawed vertebrates appeared in the latest Ordovician and became common in the Devonian, often known as the "Age of Fishes".[27] The two groups of bony fishes, the actinopterygii and sarcopterygii, evolved and became common.[28] The Devonian also saw the demise of virtually all jawless fishes, save for lampreys and hagfish, as well as the Placodermi, a group of armoured fish that dominated the entirety of that period since the late Silurian. The Devonian also saw the rise of the first labyrinthodonts, which was a transitional form between fishes and amphibians.
Mesozoic vertebrates
Amniotes branched from labyrinthodonts in the subsequent Carboniferous period. The Parareptilia and synapsid amniotes were common during the late Paleozoic, while diapsids became dominant during the Mesozoic. In the sea, the bony fishes became dominant; the birds, a derived form of dinosaurs, evolved in the Jurassic.[29] The demise of the non-avian dinosaurs at the end of the Cretaceous allowed for the expansion of mammals, which had evolved from the therapsids, a group of synapsid amniotes, during the late Triassic Period.
After the Mesozoic
The Cenozoic world has seen great diversification of bony fishes, frogs, birds and mammals.
Over half of all living vertebrate species (about 32,000 species) are fish (non-tetrapod craniates), a diverse set of lineages that inhabit all the world's aquatic ecosystems, from snow minnows (Cypriniformes) in Himalayan lakes at elevations over 4,600 metres (15,100 feet) to flatfishes (order Pleuronectiformes) in the Challenger Deep, the deepest ocean trench at about 11,000 metres (36,000 feet). Fishes of myriad varieties are the main predators in most of the world's water bodies, both freshwater and marine. The rest of the vertebrate species are tetrapods, a single lineage that includes amphibians (with roughly 7,000 species); mammals (with approximately 5,500 species); and reptiles and birds (with about 20,000 species divided evenly between the two classes). Tetrapods comprise the dominant megafauna of most terrestrial environments and also include many partially or fully aquatic groups (e.g., sea snakes, penguins, cetaceans).
Classification
There are several ways of classifying animals. Evolutionary systematics relies on anatomy, physiology and evolutionary history, which is determined through similarities in anatomy and, if possible, the genetics of organisms.[30] Phylogenetic classification is based solely on phylogeny.[31] Evolutionary systematics gives an overview; phylogenetic systematics gives detail. The two systems are thus complementary rather than opposed.[32]
Traditional classification

Conventional classification has living vertebrates grouped into seven classes based on traditional interpretations of gross anatomical and physiological traits. This classification is the one most commonly encountered in school textbooks, overviews, non-specialist, and popular works. The extant vertebrates are:[12]
Subphylum Vertebrata
Class Agnatha (jawless fishes)
Class Chondrichthyes (cartilaginous fishes)
Class Osteichthyes (bony fishes)
Class Amphibia (amphibians)
Class Reptilia (reptiles)
Class Aves (birds)
Class Mammalia (mammals)
In addition to these, there are two classes of extinct armoured fishes, the Placodermi and the Acanthodii.
Other ways of classifying the vertebrates have been devised, particularly with emphasis on the phylogeny of early amphibians and reptiles. An example based on Janvier (1981, 1997), Shu et al. (2003), and Benton (2004)[33] is given here:
Subphylum Vertebrata
Palaeospondylus
Superclass Agnatha or Cephalaspidomorphi (lampreys and other jawless fishes)
Infraphylum Gnathostomata (vertebrates with jaws)
Class †Placodermi (extinct armoured fishes)
Class Chondrichthyes (cartilaginous fishes)
Class †Acanthodii (extinct spiny "sharks")
Superclass Osteichthyes (bony vertebrates)
Class Actinopterygii (ray-finned bony fishes)
Class Sarcopterygii (lobe-finned fishes, including the tetrapods)
Class Amphibia (amphibians, some ancestral to the amniotes)- now a paraphyletic group
Class Synapsida (mammals and the extinct mammal-like reptiles)
Class Sauropsida (reptiles and birds)
While this traditional classification is orderly, most of the groups are paraphyletic, i.e. do not contain all descendants of the class's common ancestor.[33] For instance, descendants of the first reptiles include modern reptiles, as well as mammals and birds. Most of the classes listed are not "complete" (and are therefore paraphyletic) taxa, meaning they do not include all the descendants of the first representative of the group. For example, the agnathans have given rise to the jawed vertebrates; the bony fishes have given rise to the land vertebrates; the traditional "amphibians" have given rise to the reptiles (traditionally including the synapsids, or mammal-like "reptiles"), which in turn have given rise to the mammals and birds. Most scientists working with vertebrates use a classification based purely on phylogeny, organized by their known evolutionary history and sometimes disregarding the conventional interpretations of their anatomy and physiology.
Phylogenetic relationships
In phylogenetic taxonomy, the relationships between animals are not typically divided into ranks, but illustrated as a nested "family tree" known as a phylogenetic tree. The one below is based on studies compiled by Philippe Janvier and others for the Tree of Life Web Project and Delsuc et al.[34][35]

Vertebrata/

Agnatha/

Hyperoartia (lampreys)
MyxiniCyclostomes
?†Euconodontaunnamed

†Pteraspidomorphi
?†Thelodontiunnamed

?†Anaspidaunnamed

†Galeaspidaunnamed

?†Pituriaspida
†OsteostraciGnathostomata

†Placodermi (armoured fishes)unnamed

Acanthodians, incl. Chondrichthyes (cartilaginous fishes)Euteleostomi

Actinopterygii (ray-finned fishes)Sarcopterygii(lobe-finnedfish)

?†Onychodontiformes
Actinistia (coelacanths)unnamed

†Porolepiformes
Dipnoi (lungfishes)unnamed

†Rhizodontimorpha

†Tristichopteridae
TetrapodaCraniata
Number of extant species
The number of described vertebrate species are split evenly between tetrapods and fish. The following table lists the number of described extant species for each vertebrate class as estimated in the IUCN Red List of Threatened Species, 2014.3.[36]

The IUCN estimates that 1,305,075 extant invertebrate species have been described,[36] which means that less than 5% of the described animal species in the world are vertebrates.
Vertebrate species databases
The following databases maintain (more or less) up-to-date lists of vertebrate species:
Fish: Fishbase
Amphibians:
Reptiles: Reptile Database
Birds:
Mammals:
Reproductive systems
Nearly all vertebrates undergo sexual reproduction. They produce haploid gametes by meiosis. The smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova. These fuse by the process of fertilisation to form diploid zygotes, which develop into new individuals.
Inbreeding
During sexual reproduction, mating with a close relative (inbreeding) often leads to inbreeding depression. Inbreeding depression is considered to be largely due to expression of deleterious recessive mutations.[37] The effects of inbreeding have been studied in many vertebrate species.
In several species of fish, inbreeding was found to decrease reproductive success.[38][39][40]
Inbreeding was observed to increase juvenile mortality in 11 small animal species.[41]
A common breeding practice for pet dogs is mating between close relatives (e.g. between half- and full siblings).[42] This practice generally has a negative effect on measures of reproductive success, including decreased litter size and puppy survival.[43][44][45]
Incestuous matings in birds result in severe fitness costs due to inbreeding depression (e.g. reduction in hatchability of eggs and reduced progeny survival).[46][47][48]
Inbreeding avoidance
As a result of the negative fitness consequences of inbreeding, vertebrate species have evolved mechanisms to avoid inbreeding. Numerous inbreeding avoidance mechanisms operating prior to mating have been described.
Toads and many other amphibians display breeding site fidelity. Individuals that return to natal ponds to breed will likely encounter siblings as potential mates. Although incest is possible, Bufo americanus siblings rarely mate.[49] These toads likely recognize and actively avoid close kins as mates. Advertisement vocalizations by males appear to serve as cues by which females recognize their kin.[49]
Inbreeding avoidance mechanisms can also operate subsequent to copulation. In guppies, a post-copulatory mechanism of inbreeding avoidance occurs based on competition between sperm of rival males for achieving fertilization.[50] In competitions between sperm from an unrelated male and from a full sibling male, a significant bias in paternity towards the unrelated male was observed.[50]
When female sand lizards mate with two or more males, sperm competition within the female's reproductive tract may occur. Active selection of sperm by females appears to occur in a manner that enhances female fitness.[51] On the basis of this selective process, the sperm of males that are more distantly related to the female are preferentially used for fertilization, rather than the sperm of close relatives.[51] This preference may enhance the fitness of progeny by reducing inbreeding depression.
Outcrossing
Mating with unrelated or distantly related members of the same species is generally thought to provide the advantage of masking deleterious recessive mutations in progeny[52] (and see Heterosis). Vertebrates have evolved numerous diverse mechanisms for avoiding close inbreeding and promoting outcrossing[53] (and see Inbreeding avoidance).
Outcrossing as a way of avoiding inbreeding depression, has been especially well studied in birds. For instance, inbreeding depression occurs in the great tit when the offspring are produced as a result of a mating between close relatives. In natural populations of the great tit (Parus major), inbreeding is avoided by dispersal of individuals from their birthplace, which reduces the chance of mating with a close relative.[54]
The purple-crowned fairywren females paired with related males may undertake extra-pair matings that can reduce the negative effects of inbreeding. However, there are ecological and demographic constraints on extra pair matings. Nevertheless, 46% of broods produced by incestuously paired females contained extra-pair young.[48]
Southern pied babblers (Turdoides bicolor) appear to avoid inbreeding in two ways. The first is through dispersal, and the second is by avoiding familiar group members as mates.[55] Although both males and females disperse locally, they move outside the range where genetically related individuals are likely to be encountered. Within their group, individuals only acquire breeding positions when the opposite-sex breeder is unrelated.
Cooperative breeding in birds typically occurs when offspring, usually males, delay dispersal from their natal group in order to remain with the family to help rear younger kin.[56] Female offspring rarely stay at home, dispersing over distances that allow them to breed independently, or to join unrelated groups.
Parthenogenesis
Parthenogenesis is a natural form of reproduction in which growth and development of embryos occur without fertilization.
Reproduction in squamate reptiles is ordinarily sexual, with males having a ZZ pair of sex determining chromosomes, and females a ZW pair. However, various species, including the Colombian Rainbow boa (Epicrates maurus), Agkistrodon contortrix (copperhead snake) and Agkistrodon piscivorus (cotton mouth snake) can also reproduce by facultative parthenogenesis -that is, they are capable of switching from a sexual mode of reproduction to an asexual mode- resulting in production of WW female progeny.[57][58] The WW females are likely produced by terminal automixis.
Mole salamanders are an ancient (2.4-3.8 million year-old) unisexual vertebrate lineage.[59] In the polyploid unisexual mole salamander females, a premeiotic endomitotic event doubles the number of chromosomes. As a result, the mature eggs produced subsequent to the two meiotic divisions have the same ploidy as the somatic cells of the female salamander. Synapsis and recombination during meiotic prophase I in these unisexual females is thought to ordinarily occur between identical sister chromosomes and occasionally between homologous chromosomes. Thus little, if any, genetic variation is produced. Recombination between homeologous chromosomes occurs only rarely, if at all.[60] Since production of genetic variation is weak, at best, it is unlikely to provide a benefit sufficient to account for the long-term maintenance of meiosis in these organisms. However, meiosis may have been maintained during evolution by the efficient recombinational repair of DNA damages that meiosis provides, an advantage that could be realized at each generation.[61]
Self-fertilization
The mangrove killifish (Kryptolebias marmoratus) produces both eggs and sperm by meiosis and routinely reproduces by self-fertilisation. The capacity for selfing in these fishes has apparently persisted for at least several hundred thousand years.[62] Each individual hermaphrodite normally fertilizes itself when an egg and sperm that it has produced by an internal organ unite inside the fish's body.[63] In nature, this mode of reproduction can yield highly homozygous lines composed of individuals so genetically uniform as to be, in effect, identical to one another.[64][65]  Although inbreeding, especially in the extreme form of self-fertilization, is ordinarily regarded as detrimental because it leads to expression of deleterious recessive alleles, self-fertilization does provide the benefit of fertilization assurance (reproductive assurance) at each generation.[64]
See also
Marine vertebrate
Skeletal system of the horse
Taxonomy of the vertebrates (Young, 1962)

Bibliography

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