text:
Montgomery showing it's on the right path to wins
Chris Masse
cmasse@sungazette.com
Cameron Yeagle jumped high, stretching his right arm as far as it could go before slapping the basketball back in play and saving a Montgomery possession.
Only 20 seconds remained last Friday against Northeast Bradford and Montgomery trailed by 25, but the Red Raiders had not backed down all night and certainly were not going to give in now. It is early, much work remains and growing pains likely will occur, but that play and so many other hustling ones like it provide Montgomery with something it has lacked the last few years:
Montgomery opened its season losing to Northeast Bradford and South Williamsport at the Kyle Lynn Memorial Tournament, but the tenacity and will with which it played provide strong building blocks. This is a program that has one win over the past two seasons and that went winless a season ago. Making NEB and South earn their wins the hard way already shows improvement and if Montgomery plays with that kind of intensity every game, the wins will start coming.
It is a process, but Montgomery is showing growth and letting opponents know that it will not be rolling over any time soon.
"They believe in what we're running, they believe in the system," first-year coach Junior Parrish said following the season-opening 55-30 loss against NEB. "I told them just now we're going to be taking steps all year that you guys don't even recognize until the end of the year and then it's just moving forward from there. I think we're going in the right direction."
It certainly appeared that way against NEB. The Panthers return four starters from last year's team that reached the Class AA state tournament's second round. They have size, quickness, shooters and chemistry and buried Montgomery early in the first quarter a year ago. This time, a team featuring just two returning starters, stayed with NEB most of the night, trailing 28-17 at halftime. NEB opened a 20-point third-quarter lead, but Montgomery fought back and pulled within 14 early in the fourth.
It was a similar story the next day against South Williamsport. The Raiders trailed by only eight at halftime and still were within striking distance early in the fourth quarter.
Sure, Montgomery would like more than moral victories, but fighting back against a quality opponent marks a crucial rung climbed up the ladder. The Raiders had their chances, especially early against NEB, running good sets and working for quality shots. They simply missed a lot of those shots. And that is OK because those are things that are fixable as the year continues.
"I'm not worried about that (effort) with this team. This team is going to fight. The energy in practice is totally different," Parrish said. "The biggest thing with this team is just learning the techniques of the game. In the first half we had open shot after open shot. The only complaint I have is grab a rebound and box out. But we had 13 turnovers and they only scored two points off those so to me that is effort. That's them saying, 'I messed up, so let's get back and make up for it.'"
Senior forward Steve Prince provided fantastic leadership last fall for a young football team and was key in it rallying from an 0-4 start to finish 4-6. He is playing a similar role now and setting a tone at practice each day. Instead of sulking about winning only three games in three seasons, Prince is doing all he can to make this last season a memorable one. His teammates are falling in line, too, and this could become a season that leads to bigger things.
It helps having pieces like sophomores Logan Almeida and Maurice Walters to build around. Almeida is building off a promising freshman season and produced eight points, six rebounds and four assists against NEB. Walters added 10 points and seven rebounds. Freshman Rayne Parrish hit a 3-pointer that sparked a late third-quarter push, sophomore Austin Kuhn buried a 3-pointer that made it a nine-point game late in the first half and sophomore Coltin Hans attacked defensively.
The pieces are there, the confidence is growing and, even without a win yet, Montgomery already looks like a different team.
"My biggest thing with this team is we have the athletes and they have to believe in themselves and not just rely on one or two players. We have to bring it and play team defense and team rebounding," Parrish said. "We're just missing those plays. The points we're losing by we're beating ourselves … but it's coming."
South Williamsport easily could have pointed toward its youth when explaining its opening-night 52-42 loss against North Penn-Liberty. Coach Rob Houseknecht, though, will not take that bait. Yes, the Mounties lost four starters from last year's District 4 Class AA semifinalist and are playing mostly sophomores and freshmen. Still, the expectations remain the same. South defeated Class A title contender St. John Neumann in a scrimmage and now it is a matter of building off Saturday's win and showing that, while the names have changed, the results don't have to.
Like Montgomery, having players going all out provides a plus in that pursuit. Senior point guard Ethan Laudenslager dazzled with 17 points, 11 rebounds and five assists, but several newcomers also made an impact. Noah Persun brought the defensive energy, Landon Sanford scored nine points off the bench, freshman Lee Habalar grabbed five rebounds and Port Habalar delivered some key second-half plays.
"When I tried to get them to go and go they were out there diving for loose balls. They're putting their effort into it and it's great to see," Houseknecht said. "That's something that's hard to coach and I'm glad to see that they are going after it like that."
PUTBACKS
North Penn-Liberty looks like a potential District 4 Class A title contender and excelled in pressure-filled moments as it captured the Kyle Lynn Memorial Tournament for a second consecutive year. A night after dominating the final four minutes against South, North Penn-Liberty edged Northeast Bradford, a team with four starters back from last year's Class AA second round state tournament participant, 46-44. Point guard Noah Spencer earned MVP honors and produced 14 points, 10 rebounds and six assists against South … Canton won the Galeton Tournament title in impressive fashion, routing Galeton and Williamson by 65 combined points. Twelve players scored in the semifinals and 10 did so against Williamson. This is a balanced and deep team and four players reached double figures … Nick Shedleski scored 23 points, helping Lewisburg take third at the Knights of Columbus Tournament in Shamokin with a 60-35 win against Shenandoah Valley … Joe Grab helped Wellsboro rally past North Penn-Mansfield, 58-54, as it took third at the Loyalsock Tournament. Grab scored a career-high 26 points and added six rebounds and five assists. North Penn-Mansfield's Logan Tokarz scored a career-high 16 points in the opener against Loyalsock.
Dr. Masse's Top 5 Boys Basketball Teams
1. Montoursville (1-0)
The Warriors have not had a lot of time working together after the football team's successful and lengthy postseason run, but opened the season with a win against a Warrior Run team that could turn some heads in Class AAA. Montoursville faces a good early-season schedule featuring upcoming games against Central Columbia, Lewisburg, Loyalsock and Lourdes before Christmas. Obviously, a team with all but one starter back from last year's 19-win team will be tested early and that could help it as the season progresses.
2. Loyalsock (2-0)
Four starters are gone from last year's District 4 Class AAA champion, but Loyalsock wasted little time showing why it remains a serious title contender. Loyalsock captured its Tip-Off Tournament for a third straight season, scoring 181 points in blowout wins against North Penn-Mansfield and Whitehall. The Lancers opened their season with 98 points against North Penn-Mansfield as four players scored in double figures. Aiden Gair and Rees Watkins are the known commodities on this team, but players like Saraj Ali, Idris Ali and Sean Jensen also showed their upside and produced strong performances.
3. Hughesville (1-0)
A young Spartan team often put two or three good quarters together last season, but sometimes struggled late in heartbreaking losses. What a big step it was then for the Spartans to go to St. John Neumann Friday, start strong and hold off repeated comeback attempts while winning a 73-67 thriller. That was an important hurdle to jump over and the Spartans did it with a strong collective effort. This is a deep team and both starters and reserves made big impacts. Justus Leighow sparked the defense and also scored a career-high 18 points. Blake Sherwood scored 16 points in 12 minutes and guard Clayton Poust added 15. Hughesville overcame foul trouble, a tough environment and a quality opponent with two freshmen also providing key minutes. This is a proud program that does not revel in early-season wins, but if this was a sign of things to come, then it was quite a start.
4. St. John Neumann (0-1)
And from Neumann's perspective, many positives also can be taken. Start with freshman Davion Hill erupting for 37 points in his first high school game. No area freshman has opened his scholastic career quite like that during the 2000s and one can only wonder how much better he can get from here. The Knights have only two starters back from last year's 20-win team but did not buckle after Hughesville's quick start. Like Hughesville, this is a program that defines itself not with December wins but with postseason championships. This was a loss, but it also is a game that could help the Knights reach their goals as the season progresses.
5. Sullivan County (2-0)
Returning a strong core from a Class A state qualifier, Sullivan County showed why this could be another exciting season by winning its Mountain Madness Tournament. The Griffins defeated Troy, 59-45 in the final after blasting MMI Prep, 60-36. Balance and depth could be strengths this season and at least three players scored in double figures in both games. Forward Jesse Williams is becoming a weapon inside and opening up the outside for guards who drained nine second-half 3-pointers against MMI Prep. Jalen Thomas dealt eight assists in that game and Justin Metzger scored 21 points in both.
Aiden Gair, Loyalsock
Sam Carpenter, Sullivan County
Gair went bonkers in his first two games, reaching career-highs both nights and torching Whitehall for 41 points in the final. Gair did damage outside and inside, making 12 3-pointers, including eight against Whitehall. Gair is the lone returning starter back from last year's team and showed he is eager to embrace his new leadership role. Carpenter also is a quality senior leader and averaged 16 points in Sullivan County's win, playing well on both ends. He earned Tournament MVP honors and scored 18 points while adding seven rebounds and four steals against Troy.
Millville at St. John Neumann
It is early, but today's showdown could go a long way in determining this year's Mid-Penn Conference champion. These long-time rivals split the championship last season, each going 13-1 in league play. Neumann has earned at least a share of seven straight league championships and Millville a share of the last two. The Quakers captured last year's District 4 Class AA champion and it and Neumann both reached the second round of states. The road team won each game last year and this will be an outstanding early-season test for both squads.
Masse may be reached at cmasse@sungazette.com. Follow him on Twitter at @docmasse.
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State title run highlights big hockey season for Albion junior
By Mike Wertman, Sports Writer Posted 31 March 2014 at 12:00 am
Contributed Photo – Albion High junior Monica Benjovsky helped the Monroe County Youth Hockey Edge U16 team reach the state finals.
Capping off a memorable season, Albion High junior Monica Benjovsky recently helped lead the Monroe County Youth Hockey Edge U16 team to the New York State Amateur Hockey state championships.
Monica, who plays defense, is in her third year with the Edge which lost to Potsdam in the state championship game.
Seeded No. 1 from the West Division, the Edge went 2-1 in the opening round of the tournament of the state tournament, then defeated defending champion St. Lawrence 2-1 in the semifinals before dropping a 3-1 decision to Potsdam in the finals.
"They are the greatest group of girls and I have amazing coaches," said Monica of her Edge team. "Playing with them has been enjoyable every step of the way. A great moment was the championship game in the New York State Amateur Hockey League State Tournament. It was a good hard fight and I am so very proud of the determination and commitment of my team. We played our hearts out. Such a good memory."
Monica, who also plays varsity soccer and tennis at Albion High, has been enjoying skating on the ice for virtually all of her life.
"I started skating with my older sister Kali and twin brother Dyer when I was 3," she said. "My grandpa had purchased my sister some figure skates. She wanted to take figure skating lessons, so we all took learn to skate lessons at the same time. We have an older cousin, whom we have always idolized, that plays hockey. Once my twin brother Dyer and I learned how to skate, we thought that we might like to be like our cousin Kyle and play hockey too. Dyer and I started playing hockey when we were 5."
And Monica, who is also talented in the classroom ranking 11th in her class, credits her close ties with her twin brother as key in keeping her involved with and enthused about playing hockey.
" Funny story, just shorty after I started hockey, when I was probably 6 or 7, I had decided that I didn't really want to play anymore. BUT!!!, I felt that couldn't quit because I would be letting Dyer down. At the time, I felt like I needed to take care of him and that he needed me," she said. "It wasn't the case of course, but I like to mother him, haha. I am so thankful that I didn't give in to my feelings on not letting Dyer down, otherwise, I wouldn't be playing today. I played on the same team with him and his friends until I was 14. The majority of the boys on that team have stayed together until this very day. I became so close to them, consider them family, and will always cherish those memories with that team."
Contributed Photo – Monica Benjovsky in action for the Edge U16 team.
And though she plays other sports, Monica's heart certainly belongs with hockey.
"This might sound corny, but I love the feel of the ice on my blades, the sound the blades make on the ice, the smell of the fresh cut ice, the coolness of the rink", she said. "It's in my blood, I crave those feelings. I love the physical demands of the sport, to be in shape, to push myself to the next level, to keep pushing regardless of how tired I am. I love the bonds that I make with my teammates and their families. I love my teammates families. I love the game itself. There is literally no greater game that the game of hockey. "
She also credits one of her long-time coaches for her success on the ice.
"I had a coach for a number of years when playing with the boys that has been the most influential person in my hockey career. His name is Coach Adam Driscoll. He is my favorite memory and favorite coach from all my years in hockey," said Monica. "He gave me so much confidence in my abilities. He has so much faith in what I can accomplish. To this day,, he still takes interest in my hockey and supports my endeavors. He is a incredible person and an incredible role model as well."
Monica, who is now busy practicing with the Albion High tennis squad along with her brother Dyer and sister Kali, looks forward to continuing her career on the ice.
"I hope to continue with the Edge girls team for the 2014/15 hockey season," she said. "The year after that, I plan to attend college with hopes of playing ladies hockey for a college. "
Monica, whose edge team played in both the Great Lakes Girls Hockey League in Western New York and the Lower Lakes Female Hockey League in Canada this season, will be attending a Rush Hockey Showcase in Toronto in June, a Rush Hockey Camp in Toronto in June and the Boston Bean Town Classic Showcase Tournament in July.

redpajama_set_name: RedPajamaCommonCrawl


Are you tired of hearing "don't skip breakfast?" This is because breakfast is the most important meal in the day, it should not be missed. The literal meaning of the word "breakfast," is to break the fast between dinner and the meal eaten after a person wakes up the next morning. About 18 percent of males and 13 percent of females between the ages of 35 and 54 are breakfast skippers, according to a 2011 study by the market research company NPD group.
For most people, it can be up to 12 hours since their last meal, and yet they are quick to skip it as they rush out the door.
Eggs: Including an egg or two for breakfast may require a few extra minutes of preparation time, but the potential health benefits make them worth cooking and eating. Not only are eggs packed with protein and amino acids, they are also one of the few significant sources of vitamin D, which is important for absorbing calcium for stronger bones. You can have two boiled eggs with avocado and cucumber, and green tea; or have it fried with olive oil and enjoy it.
Whole grains: Whether you are taking them in the form of bread, cereal or oatmeal, breakfast is one of the best times to enjoy whole grains in your meal. This super-food is a great source of fiber, which is essential for a healthy heart and digestive tract, and can help reduce the risk of heart disease, cancer and diabetes. You can top your oatmeal with strawberries or slice banana and pour nourishing almond milk in it.
Whether you are in class or on the job or even just going for a visit, the last thing you want on your mind is food, because once the thought of a hearty bowl of cereal with a side of fruit yogurt enters your brain, there is no use trying to focus on anything else. By eating breakfast every morning, you are able to be more focused and productive until it's time to refuel at lunch. But when you skip out on breakfast, it's hard not to think about food, especially with a noisy stomach that needs to be fed.
Feeling cranky during the morning is understandable – you probably wanted to stay in bed for a few extra winks. You don't feel like going to work, and what most people forget, you're starving! Imagine going without food for 8 to 12 hours during the day; you probably won't be the most approachable person in the office or classroom. Do yourself, your classmates and your co-workers a favor by eating breakfast to help you deal with any morning moodiness and stress.
of it after you have had lunch. Some people will even skip lunch after they must have had breakfast. But this depends on the kind of breakfast you had.
When you are asleep, your body isn't burning as many calories as you need to. If you delay your first meal of the day till lunch, your body goes into survival mode and starts storing calories, creating fat which many people are scared of. Do yourself a favor and take the time to have breakfast so your body doesn't think you are starving and needlessly store calories.
One truthful fact about you skipping your breakfast is that you end up overeating. If you prolong the amount of time between dinner and your next meal of the day, it's only natural that you end up eating more than you should. The thought of food all morning will only cause you to gorge at lunch, eating extra calories that can lead to obesity and other health complications.
can lead you to ignore your nutrition by satisfying hunger cravings with fatty foods anytime you like.
• First, you slow down your metabolism.
• Second, fat is stored longer in your body.
• Third, you have a higher tendency to overeat at your next meal.
• Fourth, you gain weight and your LDL cholesterol goes up.
• Obesity is bad for health and it can trigger heart problem.
Don't let a shortage of time keep you from enjoying a bite to eat upon waking up. Start the day off with a healthy and delicious meal. You can even indulge a bit with some crispy bacon, sausage links or pancakes. Just make sure to have something with a high nutritional value on the side like a bowl of fresh strawberries.
One of the greatest benefits of eating breakfast every morning is you can lose weight by doing so. Numerous studies have also shown that an increase in weight is commonly associated with skipping breakfast. The best part is, even if you eat too much or have something a little unhealthy, you still have the entire day to make up for it. Eating breakfast every morning is one of the easiest ways to lose weight and eat healthier.


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Doug Cameron (politician) FAQs 2019- Facts, Rumors and the latest Gossip.
Doug Cameron (politician) FAQs: Facts, Rumors, Birthdate, Net Worth, Sexual Orientation and much more!
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Douglas Niven Cameron (born 27 January 1951) is an Australian politician and trade unionist. He has been a Labor member of the Australian Senate since July 2008 representing the state of New South Wales. Cameron was born in Bellshill Scotland. He was first elected to the Senate at the 2007 federal election. He won Labor preselection by mounting a successful challenge to then incumbent Senator George Campbell.
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Doug Cameron was born on the 27th of January 1951 , which was a Saturday. Doug Cameron will be turning 69 in only 281 days from today.
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Doug Cameron is 68 years old. To be more precise (and nerdy), the current age as of right now is 24844 days or (even more geeky) 596256 hours. That's a lot of hours!
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Added on December 5, 2022 Press Trust of india
SC junks PIL to remove 'wrong' historical facts on Taj Mahal
New Delhi: The Supreme Court on Monday refused to entertain a plea seeking removal of alleged wrong historical facts related to the construction of the Taj Mahal from history books and find the age of the monument.
A bench of Justices M R Shah and C T Ravikumar asked the petitioner to approach the Archaeological Survey of India (ASI) and make a representation before it.
"The PILs are not meant for fishing enquiry. We are not here to reopen history.Let history continue.The writ petition is dismissed as withdrawn. The petitioner is granted liberty to make representation to the ASI. We have not expressed any merits on the same," the bench said.
The top court was hearing a plea filed by Surjit Singh Yadav seeking direction to the Centre to remove the alleged wrong historical facts related to the construction of the Taj Mahal from history books and textbooks.
The plea also sought directions to the ASI to carry out a probe into the age of the Taj Mahal.
The petitioner contended that his research shows that a magnificent mansion already existed at the site where the body of Mughal emperor Shah Jahan's wife Mumtaz Mahal was placed in a dome-like structure.
"It is extremely strange why all the court chroniclers of Shah Jahan have not mentioned the name of the architect of this magnificent mausoleum. Therefore, this quite clearly indicates that the mansion of Raja Man Singh was not demolished but only modified and renovated to create the current look of the Taj Mahal. That is why there is no mention of any architect in the accounts of the court chroniclers of Shah Jahan," the plea submitted.
The 17th century monument is a UNESCO World Heritage Site.


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This issue includes topics such as aircraft separation, loss of situational awareness, navigation errors, altitude deviations, and traffic-alert and collision avoidance system resolution advisories. The International Civil Aviation Organization's Regional Aviation Safety Group–Pan America lists MAC is one of its top safety priorities.
Recent Fatal Accidents
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Source: Aviation Safety Network
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The helicopter landed safely.
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NTSB presses for new training and wider use of technology to help avert midair collisions.
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An air traffic control breakdown placed an airliner and a military transport on a collision…


"The public cannot be too curious concerning the characters of public men," said Samuel Adams, one of the most important figures in the founding of our country.
"In selecting men for office, let principle be your guide. Regard not the particular sect or denomination of the candidate—look to his character..." --Noah Webster.
Recently the public has had another chance to evaluate the character of Hillary Clinton. She previously claimed she landed under fire at the Tuzla airport in war-torn Bosnia in 1996. "I remember landing under sniper fire," she said. "There was supposed to be some kind of a greeting ceremony at the airport, but instead we just ran with our heads down to get into the vehicles to get to our base." Last week viewers of YouTube saw visual evidence to the contrary. Film of her arrival in Bosnia shows no evidence of anyone frightened or running with head down. People were smiling and waving, posing for pictures, and there was even time for a Muslim girl to read a poem to Hillary and receive a kiss from her.
That's not the first of Hillary's lies, nor is it likely to be the last. Her own book says she was on the soccer team in high school. But the school she attended had no soccer team when she attended.
She claimed daughter Chelsea went for a jog to the World Trade Towers on 9/11, saw the planes hit, and was nearly in danger. But Chelsea in a magazine article debunked her mother story, saying she was on the other side of New York and was awakened by a phone call on 9/11 telling her to watch the news.
Hillary also claims she was named after Sir Edmund Hillary, conqueror of Mount Everest. But when she was born, he was a New Zealand beekeeper nobody had ever heard of. He didn't scale the mountain until 1953. She was born in 1947.


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CBSE Class IX (9th) Science | Chapter 9. FORCE AND LAWS OF MOTION | Solved Exercises
Question 1. An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with a non-zero velocity? If yes, state the conditions that must be placed on the magnitude and direction of the velocity. If no, provide a reason.
Answer : Yes, it possible for an object to be traveling with a non-zero velocity, if the object experiences a net zero external unbalanced force.
This is due to inertia of motion. If the body is initially moving with some velocity, on a fine surface, then it will continue to move with the same velocity for some time, though the net external force acting on the body is zero. For example, when we stop pedaling a moving cycle, the bicycle continues to move for some time with a non-zero velocity, without application of a net zero external unbalanced force. After some time, the cycle slows down gradually and finally comes to rest due to force of friction and air resistance, acting in the opposite direction of motion. In the absence of unbalanced forces of ground friction and air resistance, acting in the opposite direction of motion, the bicycle will remain in motion for ever.
Question 2. When a carpet is beaten with a stick, dust comes out of it. Explain.
Answer : When a carpet is beaten with a stick, its state of rest gets changed into state of motion. Where as the dust particles, which are loosely attached to its surface, try to remain in state of rest, due to static inertia, therefore get detached from the surface of carpet.
Question 3. Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Answer : At the event of sudden change in speed or direction of the bus, when driver applies accelerator or brakes or steer it along the sharp curve on the road, the luggage kept on the roof tend to remain in its last position due to its state of inertia, which may be of either rest or of motion. This may result in, luggage being either falling in the backward direction or in forward direction or spinning off on the sharp road turns. Therefore,to prevent this, it advised to tie the luggage kept on the roof of a bus with a rope.
Question 4. A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.
Answer : (c) there is a force on the ball opposing the motion . Explanation : A cricket ball after getting hit by batsman, slows down and comes to rest due to forces of ground friction and air resistance acting in the opposite direction.
Question 5. A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 tonnes (Hint: 1 tonne = 1000 kg.)
Answer :
Given here
Distance, s =400 m
Initial Speed, s = 0 ms-1
Time, t = 20 s
Acceleration a = ?
As we know Distance, s = ut+ ½ (at2)
Substituting the values in the above expression
400 m =0 ms-1× 20s + ½ a &times (20s)2
=> 400 m = a × 200 s2
=> a = 400 m /200 s2 = 2 ms-2
Now we have to calculate the force by using the relation F = ma Here, m = 7 tonnes = 7 × 1000 kg, a = 2 ms-2
∴ F = 7000 kg × 2 ms-2
= 14000 kg ms-2
=14000 N
So, the force acting on the truck is 14000 N
Question 6. A stone of 1 kg is thrown with a velocity of 20 m s–1 across the frozen surface of a lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice?
Mass (m) = 1 kg
Initial Velocity (u) =20 ms-1
Total distance traveled (s) =50 m
Force of friction, (F) = ?
From the equation of motion, we have
v2 − u2 = 2as
=> 2as =(v2 − u2)
=> 2a×50 m =02 − (20 ms-1)-2
=> a = −400 m2s−2/ 100 m
=> = − 4ms−2
From Newton's second law of motion
=> Force (F) = mass(m) × acceleration(a)
=> F = 1 kg ×− 4ms−2
=> = − 4 kg ms−2 = −4 N Ans
Negative sign represents force of friction acting in opposite direction
Question 7. A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:
(a) the net accelerating force;
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2.
(a) Force exerted by the engine = 40,000 N
Frictional Force offered by the track in opposite direction = 5,000 N
The net accelerating force, F = 40,000 N − 5,000 N
= 35,000 N
(b) Mass of the train, m = 5 × 2,000kg + 8,000 kg
=18,000 kg
From Newton's second law of motion, acceleration
a = F/m = 35,0000 N / 18,000 kg
= 35 kg ms-2/ 18 kg
= 1.94 ms-2
(c) The force exerted by wagon 1 on wagon 2
= mass of 4 wagons behind wagon 1 × acceleration
= 8,000 kg × 1.94 ms−2
= 15,520 N Ans.
Question 8. An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 ms−2 ?
As given
Mass of vehicle, m = 1,500 kg
Acceleration(Negative) = −1.7 ms−2
The force to be applied
between the vehicle and road, F
= ma
= 1500 kg × (−1.7 ms−2
= −2,550 kg ms−2
= −2,550 N Ans
Question 9. What is the momentum of an object of mass m, moving with a velocity v?
(a) (mv)2 (b) mv2 (c) mv2 (d) mv
Answer : (d) mv is correct as Momentum = mass×velocity = mv
Question 10. Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
To move wooden cabinet at a constant velocity, across the floor, the net force on cabinet should be zero
∴ Applied force + Frictional Force = Zero
∴Frictional Force + 200 N = 0
∴ Frictional Force = −200 N
Negative sign indicates the frictional force acts in the opposite direction of the applied forced. Hence, frictional force exerted on the cabinet will be 200 N
Question 11. Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
As given, Mass of each object m1=m2 = 1.5 kg.
Initial velocity of first object, u1 = 2.5 ms−1
Initial velocity of second object, u2 = 2.5 ms−1
Combined mass after the collision =m1 + m2
=1.5 kg + 1.5 kg = 3.0 kg
Let v be the velocity of the combined object after collision
By the law of conservation of momentum
Total momentum before collision = Total momentum after collision
m1u1+m2u2 =(m1+m2)v
=> 1.5 × 2.5 + 1.5 ×(&minus2.5) =(3.0)v
=> 0 = 3.0 v
Or v = 0 ms−1
∴ the combined object comes to rest after collision
Question 12. According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.
Answer : The logic given by the student is wrong as the action and reaction forces act on different bodies.
Explanation for 'why the truck does not move' is as follows : The truck being a massive object has large static inertia, due to which, a large opposing force of friction comes into play between the ground and its tires, when ever an external force is applied to move it from its position. The force applied by us on the truck is insufficient to overcome the force of friction between its tires and road, rather it is counter balanced by a part of massive frictional force. Hence the truck does not move
Question 13. A hockey ball mass 200 g travelling at 10 m s−–1 is struck by a hockey stick so as to return it along its original path with a velocity at 5 m s−1. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.
The Mass of Hockey ball, m = 200 g = 0.2 kg
Initial velocity, u = 10 ms−1
Final velocity, v = −5ms−1
Initial momentum, p1 =mu = 0.2 ×10 = 2 kg ms−1
Final momentum, p2 =mu = 0.2 ×(−5) = &minus1 kg ms−1
∴ Change in momentum =p2−p1
=&minus1 kg ms−1 − 2 kg ms−1
=− 3 kg ms−1
The negative sign shows a change in direction of hockey ball, along the return path after strike
Question 14. A bullet of mass 10 g travelling horizontally with a velocity of 150 m s−1 strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block. Also calculate the magnitude of the force exerted by the wooden block on the bullet
Mass of bullet =10 g = 0.01 kg
Initial Velocity of bullet, u = 150 ms−1
Final Velocity of bullet, v = 0 ms−1
Time taken, t =0.03 s
a =(v−u)/t
=(0 ms−1 &minus 150 ms−1)/0.03s
= − 5000 ms−2
Let the distance of penetration = s
As per equation of motion, v2 =u2+2as
=> s =(v2− u2)/2a
= [0 − (150 ms−1)2]/2×(−5000ms−2)
=(150×150 m2s−2)/2&times 5000 ms−2
= 2.25 m
∴ s = 2.25 m
The magnitude of the force exerted by the wooden block on the bullet, F
=ma
=0.01 kg ×(&minus 5000 ms−2 = 50 N
Question 15. An object of mass 1 kg travelling in a straight line with a velocity of 10 m s−1 collides with, and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.
Here, mass of object m1, velocity of object, v1= 10 ms−1
Total momentum just before the impact = m1× v1
= 1 kg × 10 ms−1
= 10 kg ms−1
Total momentum just after the impact =Total momentum just before the impact
Now, this object of mass 1 kg sticks to a stationary wooden block of mass 5 kg.
∴ combined mass of object, m2 = 1 kg + 5 kg = 6 kg
Velocity of combined object, v2 = ?
As per law of conservation of momentum
m1v1 =m2v2
=> v2 m1v1/m2
=> v2 =(1 kg) ×(10 ms−1)/ 6 kg
= 5/3 ms−1
∴ The velocity of combined object is 5/3 ms−1
Question 16. An object of mass 100 kg is accelerated uniformly from a velocity of 5 ms–−1 to 8 ms−1 in 6 s. Calculate the initial and final momentum of the object. Also, find the magnitude of the force exerted on the object.
Mass of object, m = 100 kg
Initial Velocity, ui = 5 ms−1
Final Velocity, v = 8 ms−1
Initial Momentum, p1 = mui= 500 kg ms−1
Final Momentum, p2 = mv= 800 kg ms−1
The magnitude of the force exerted on the object, F
= (p2 - p1)/ t
= (800 - 500) kg ms−1)/6 s
=300 kg ms−1/6 s = 50 N Ans.
Question 17. Akhtar, Kiran and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change in momentum as compared to the change in momentum of the motorcar (because the change in the velocity of the insect was much more than that of the motorcar). Akhtar said that since the motorcar was moving with a larger velocity, it exerted a larger force on the insect. And as a result the insect died. Rahul while putting an entirely new explanation said that both the motorcar and the insect experienced the same force and a change in their momentum. Comment on these suggestions.
Answer : As the mass of insect is much smaller than that of motorcar and after collision, the velocity of insect will be same as that of motor car ; hence change in the momentum of insect can not be more than that of the motorcar. Hnece Kiran's suggestion is wrong
Akhtar's statement is also not right; as the force is not due to larger velocity, it is due to change in momentum.
Rahul's suggestion is correct. Its being a contained collision, there is no external force on the system comprising insect and motor car; net momentum of system is conserved in the collision; hence
Δp1 + Δp2= 0
i.e. change in momentum of insect and motor car are equal and opposite. In other word action force exerted by insect on motor car is equal to reaction force exerted by motor car on insect.
Question 18. How much momentum will a dumb-bell of mass 10 kg transfer to the floor if it falls from a height of 80 cm? Take its downward acceleration to be 10 ms−2 .
Mass of dumb ball = 10 kg
Height of fall, s =80 cm = 0.8 m
Acceleration, a = 10 ms−2
Initial velocity, u = 0
Let the final velocity be = v
As v2 = u2+ 2as
=> = 0 + 2 × 10 ms−2× 0.8 m
=> = 16 m2s−2
=> v = 4 ms−1
The momentum transferred to the floor = mv
= 10 kg ×4 ms−1
Solved In text Questions - Page :118 (With in chapter)
Question 1. Which of the following has more inertia:
(a) a rubber ball and a stone of the same size?
(b) a bicycle and a train?
(c) a five rupees coin and a one-rupee coin?
Answer. (a)Clearly, given the same size of both objects, the mass of the stone is much more than that of rubber ball. Therefor, stone has more inertia than rubber
(b) Here, as train has much larger mass than bicycle, therefor train has more inertia than bicycle
(c) Here, five rupee coin has more inertia as out of two coins, five rupee coin has larger mass than one rupee coin.
Question 2. In the following example, try to identify the number of times the velocity of the ball changes: "A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team". Also identify the agent supplying the force in each case.
Answer. In the above example, the velocity of the ball changes three times. First change in velocity occurs, when A football player kicks a football to another player of his team. Second change in velocity takes place when another player kicks the football towards the goal. Third change takes place when The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team" :
All above changes in velocity of the ball, take place through two players and goalkeeper respectively as an agent supplying force.
Question 3. Explain why some of the leaves may get detached from a tree if we vigorously shake its branch
Answer.When we shake a branch of tree vigorously, we set the branch structure into sudden motion. The leaves try to toretend theirs static position due to inertia of rest. which are not as strongly attached to tree, get detached from the branch of the tree, due to sudden impulsive force
Question 4. Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?
Answer. When the bus is in motion, our speed is same as that of the bus.When a moving bus brakes to a stop, our lower part, being in contact with bus seat or floor, comes to rest, but the upper part, being not in immidiate contact with bus, tries to remain in state of motion in the forward direction, due to inertia of motion. Therefor, we fall in the forward direction.
Similiarly, when the bus accelerates from rest,our lower part, being in direct contact with bus seat or floor, comes into motion from the state of rest, where as the upper body tends to remain in state of rest due to static inertia; hence, we fall backward.
Chapter 9. FORCE AND LAWS OF MOTION | Science | CBSE Class IX (9th)
Question 1. If action is always equal to the reaction, explain how a horse can pull a cart.
Answer. As it appears, in pulling a cart, a horse exerts an equal amount of force in opposite direction to that exerted by the cart on the horse. Here forces being equal and opposite, should cancel out each other, and the cart should not move at all.
Which is, in fact, not the case, as we have seen, the cart does move, when a horse pulls it. Here the motion of cart is possible only, if horse pulls the cart with a force which is sufficient to overcome the force of friction between the cart tires and ground. When the forward reaction of horse pull on cart is greater than the backward reaction of cart pull on horse, the cart moves.
Question 2. Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity.
Answer. When a fireman uses water jet from a hose pipe to dowse the fire, the water jet, due to large amount of water, and its high velocity, has a large forward momentum. This produces an equal amount of backward momentum in the hose pipe or its supporting structure. A fire man holding the hose pipe, has to apply a matching amount of force to offset this backward momentum generated as reaction from water jet of hose pipe. Hence, it is difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity
Question 3. From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m s−–1 . Calculate the initial recoil velocity of the rifle.
Answer. As given :-
Mass of bullet, m1 = 50 g = 0.05 kg
Mass of rifle, m2 = 4 kg
Velocity of bullet, before firing, u1 = 0
Velocity of rifle, before firing, u2 = 0
Velocity of bullet, after firing, v1 = 35 m s−–1
Recoil velocity of bullet, after firing, v2 = ?
Total momentum of bullet and rifle, before firing m1u1 + m2u2 = 0
Total momentum of bullet and rifle, after firing m1v1 + m2v2 = 0
=0,05 kg × 35 ms−1 + 4 kg ×v2
= 1.75 kg ms−1 + 4 kg×v2
We know, in the absence of an external force, as per the law of conservation of momentum
Total momentum after firing = Total momentum before firing
=> = 1.75 kg ms−1 + 4 kg×v2 = 0
=> v2 = −[(1.75 kg ms−1) / 4 kg ]
=> v2 = − 0.4375 ms−1 Ans.
Negative sign shows the direction of recoil will be opposite to that of bullet
Question 4. Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s−–1 and 1 m s−–1, respectively.
They collide and after the collision, the first object moves at a velocity of 1.67 m s–1 . Determine the velocity of the second object.
Answer.
Mass of the first object, m1 = 100 g = 0.1 kg
Mass of the second object, m2 = 200 g = 0.2 kg
Before collision
Velocity of the first object, u1 = 2 m s−–1
Velocity of the second object, u2 = 1 m s−–1
After collision
Velocity of the first object, v1 = 1.67 m s−–1
Velocity of the second object, v2 = ?
As per the law of conservation of momentum
Total momentum before the collision = Total momentum after the collision
m1u1 + m2u2 = m1v1 + m2v2
=> 0.1 kg × 2 m s−–1 + 0,2 kg × 1 m s−–1 = 0.1 kg × 1.67 m s−–1 + 0.2 kg × v2
=> 0.2kg ms−–1 + 0.2kg ms−–1 = 0.167 kg ms−–1 + 0.2 kg ×v2
=> 0.4 kg ms−–1 − 0.167 kg ms−–1 = 0.2 kg ×v2
=> v2 = 0.233 Kg ms−–1 / 0.2 kg
=> v2 = 1.165 ms−–1 Ans
Hence, the velocity of second object is 1.165 ms−–1
Posted by Jagdish Singh at 03:24
HARDIK ROCKS 1 September 2013 at 10:49
very gud!!!! amazing
Sudha Menon 2 August 2014 at 14:50
Thanks , Was very helpful :) :)
Swati Ranghera 17 August 2017 at 12:06
CBSE Class IX (9th) Science | Chapter 10. GRAVITA...
CBSE Class IX (9th) Science | Chapter 9. FORCE AND...


Lake Sevan is surrounded by Geghama Mountains. It is one of the largest mountain lakes in the world, where 28 rivers are flowed, and only one originates from it. Lake Sevan is located in the central part of Armenia, at the altitude of 1900 m above sea level. Sevan is the only large lake in Armenia, one of the three important lakes that were called sea in ancient times. Lake Sevan is a freshwater lake, one of the highest in the world, and the largest in the Caucasus. There are many types of fish in the lake, but the most delicious fish is cypress, which can be tasted at a restaurant near the lake. The landscape here is diverse, with high mountains, rocky coasts, mountain forests. Lake Sevan is one of the most famous resorts in Armenia.
Tsaghkadzor is a modern ski resort located 60km north-east from Yerevan and 1845m above sea level. Tsakhkadzor is one of the most popular and hospitable resorts in Armenia. This is one of the smaller corners of our mountainous country where the beauty of nature manifests itself in all its diversity.
Everything here is for active leisure of guests: sports equipment rental, professional instructors, gym, billiards, table tennis, entertainment center, restaurant, cafe and more.
The ski season in Tsakhkadzor lasts five months, starting from mid-November to mid-April, allowing guests to enjoy the wonderful opportunities that this winter resort offers.
"Kecharis" monastic complex is a monastery complex of the XI-XIII centuries in Tsakhkadzor, built by the Pahlavuni princes. Its construction continued until the mid-XIII century. In XII-XIII centuries the monastery was one of the largest spiritual centers of Armenia and had its own school.
In 1033, Grigor Magistros built the St. Gregory the Illuminator Church. In the southern part of this church, behind a few khachkars (cross-stone), a small cross-shaped Surb Nshan cathedral is built. It was built in the 11th century and restored in 1223 by Mr. Vache. In 1203-1214, Prince Vasak Khaghbakyan built the third church in the monastery, St. Katoghikeh. There is a small rectangular chapel of XI century between St. Gregory the Illuminator and St. Nshan churches. It served as the grave of the founder of the monastery, Grigor Magistros Pahlavuni. St. Harutyun, the fourth church, located 120 meters from the monastic buildings, was built in 1220.
Saghmosavanq was seriously damaged during the earthquake.


text:
Title: Eye
Subject: ICD-9-CM Volume 3, Vision in fishes, Featured picture candidates/Eye-diagram no circles border.svg, Parietal eye, Tapetum lucidum
Collection: Eye, Sensory Organs, Visual System
Compound eye of Antarctic krill
Anatomical terminology
Eyes are the optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system.[1] Image-resolving eyes are present in molluscs, chordates and arthropods.[2]
The simplest "eyes", such as those in dark, which is sufficient for the entrainment of circadian rhythms.[3] From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.
Non-compound eyes 3.1
Pit eyes 3.1.1
Spherical lensed eye 3.1.2
Multiple lenses 3.1.3
Refractive cornea 3.1.4
Reflector eyes 3.1.5
Compound eyes 3.2
Apposition eyes 3.2.1
Superposition eyes 3.2.2
Parabolic superposition 3.2.3
Other 3.2.4
Nutrients 3.2.5
Relationship to life requirements 4
Visual acuity 5
Perception of colors 6
Rods and cones 7
Pigmentation 8
Additional Images 9
References 11.1
Bibliography 11.2
Eye of the wisent,
the European bison
Human eye.
Complex eyes can distinguish shapes and rabbits and horses, which have monocular vision.
The first proto-eyes evolved among animals about the time of the Cambrian explosion.[4] The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35[1] main phyla.[1] In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye,[5] and reducing aberrations when there is enough light.[6] The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses.[7]
Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images.
Possessing detailed hyperspectral colour vision, the Mantis shrimp has been reported to have the world's most complex colour vision system.[8] Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye.
In contrast to compound eyes, simple eyes are those that have a single lens. For example, deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents–in this way the bearers can spot hot springs and avoid being boiled alive.[9]
Evolution of the mollusc eye
Photoreception is phylogenetically very old, with various theories of phylogenesis.[10] The common origin (monophyly) of all animal eyes is now widely accepted as fact. This is based upon the shared genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago,[11][12][13] and the PAX6 gene is considered a key factor in this. The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an "arms race" [14] among all species that did not flee the photopic environment. Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel (except those of groups, such as the vertebrates, that were only forced into the photopic environment at a late stage).
Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye, and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution, despite their distant common ancestry. Phenotypic convergence of the geometry of cephalopod and most vertebrate eyes creates the impression that the vertebrate eye evolved from an imaging cephalopod eye, but this is not the case, as the reversed roles of their respective ciliary and rhabdomeric opsin classes[15] and different lens crystallins show.[16]
The very earliest "eyes", called eyespots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the light source.[1]
Through gradual change, the eyespots of species living in well-lit environments depressed into a shallow "cup" shape, the ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes.[17] However, the ancestors of modern hagfish, thought to be the protovertebrate[15] were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. This would have led to a somewhat different evolutionary trajectory for the vertebrate eye than for other animal eyes.
The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into a transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.[18]
The gap between tissue layers naturally formed a bioconvex shape, an optimally ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive power and again eased circulatory problems. Formation of a nontransparent ring allowed more blood vessels, more circulation, and larger eye sizes.[18]
There are ten different eye layouts—indeed every technological method of capturing an optical image commonly used by human beings, with the exceptions of zoom and Fresnel lenses, occur in nature.[1] Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface.[1] Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures.[1] Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomeric. These two groups are not monophyletic; the cnidaria also possess cilliated cells, [19] and some annelids possess both.[20]
Non-compound eyes
Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustaceans and cubozoa.[21]
Pit eyes
Pit eyes, also known as
Sensory organs
Anatomy of the globe of the eye
Fibrous tunic (outer)
Episcleral layer
Schlemm's canal
Epithelium
Bowman's
Stroma
Descemet's
Endothelium
Uvea/vascular tunic (middle)
Choroid
Capillary lamina of choroid
Bruch's membrane
Sattler's layer
Ciliary body
Ciliary processes
Ciliary muscle
Iris dilator muscle
Iris sphincter muscle
Retina (inner)
Inner limiting membrane
Nerve fiber layer
Ganglion cell layer
Inner plexiform layer
Inner nuclear layer
Outer plexiform layer
Outer nuclear layer
External limiting membrane
Layer of rods and cones
Retinal pigment epithelium
Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Retina ganglion cell (Midget cell, Parasol cell, Bistratified cell, Giant retina ganglion cells, Photosensitive ganglion cell) → Diencephalon: P cell, M cell, K cell, Muller glia
Foveola
Fovea centralis
Parafovea
Perifovea
Optic disc
Optic cup
Anterior segment
Anterior chamber
Aqueous humour
Posterior chamber
Capsule of lens
Zonule of Zinn
Posterior segment
Vitreous humour
Asthenopia
Keratocytes
Ocular immune system
Tapetum lucidum
Index of the eye
Evolution of the eye
Anatomy of the eye – flash animated interactive.
Webvision. The organisation of the retina and visual system. An in-depth treatment of retinal function, open to all but geared most toward graduate students.
Eye strips images of all but bare essentials before sending visual information to brain, UC Berkeley research shows
Ali, Mohamed Ather; Klyne, M. A. (1985). Vision in Vertebrates. New York:
^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad Land, M. F.; Fernald, R. D. (1992). "The evolution of eyes".
^ a b c d e Frentiu, Francesca D.; Adriana D. Briscoe (2008). "A butterfly eye's view of birds". BioEssays 30 (11–12): 1151–62.
^ "Circadian Rhythms Fact Sheet". National Institue of General Medical Sciences. Retrieved 3 June 2015.
^ Breitmeyer, Bruno (2010). Blindspots: The Many Ways We Cannot See. New York: Oxford University Press. p. 4.
^ Nairne, James (2005). Psychology. Belmont: Wadsworth Publishing.
^ Bruce, Vicki; Green, Patrick R. and Georgeson, Mark A. (1996). Visual Perception: Physiology, Psychology and Ecology. Psychology Press. p. 20.
^ BioMedia Associates Educational Biology Site: What animal has a more sophisticated eye, Octopus or Insect?
^ "Who You Callin' "Shrimp"? – National Wildlife Magazine". Nwf.org. 2010-10-01. Retrieved 2014-04-03.
^ a b c d Cronin, T. W.; Porter, M. L. (2008). "Exceptional Variation on a Common Theme: the Evolution of Crustacean Compound Eyes". Evolution Education and Outreach 1 (4): 463–475.
^ Autrum, H. "Introduction". In H. Autrum (editor). Comparative Physiology and Evolution of Vision in Invertebrates- A: Invertebrate Photoreceptors. Handbook of Sensory Physiology. VII/6A. New York: Springer-Verlag. pp. 4, 8–9.
^ Halder, G.; Callaerts, P.; Gehring, W.J. (1995). "New perspectives on eye evolution". Curr. Opin. Genet. Dev. 5 (5): 602–609.
^ Halder, G.; Callaerts, P.; Gehring, W.J. (1995). "Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila". Science 267 (5205): 1788–1792.
^ Tomarev, S.I.; Callaerts, P.; Kos, L.; Zinovieva, R.; Halder, G.; Gehring, W.; Piatigorsky, J. (1997). "Squid Pax-6 and eye development". Proc. Natl. Acad. Sci. USA 94 (6): 2421–2426.
^ Conway-Morris, S. (1998). The Crucible of Creation. Oxford: Oxford University Press
^ a b Trevor D. Lamb, Shaun P. Collin & Edward N. Pugh, Jr. (2007). "Evolution of the vertebrate eye: opsins, photoreceptors, retina and eye cup".
^ Staaislav I. Tomarev & Rina D. Zinovieva (1988). "Squid major lens polypeptides are homologous to glutathione S-transferases subunits".
^ "Eye-Evolution?". Library.thinkquest.org. Retrieved 2012-09-01.
^ a b Fernald, Russell D. (2001). The Evolution of Eyes: Where Do Lenses Come From? Karger Gazette 64: "The Eye in Focus".
^ Kozmik, Z.; Ruzickova, J.; Jonasova, K.; Matsumoto, Y.; Vopalensky, P.; Kozmikova, I.; Strnad, H.; Kawamura, S.; Piatigorsky, J.; et al. (Jul 2008). "Assembly of the cnidarian camera-type eye from vertebrate-like components" (Free full text). Proceedings of the National Academy of Sciences of the United States of America 105 (26): 8989–8993.
^ Fernald, Russell D. (2006). "Casting a Genetic Light on the Evolution of Eyes" (PDF). Science 313 (5795): 1914–1918.
^ Nilsson, Dan-E. (1989). "Vision optics and evolution".
^ Speiser, D. I.; Eernisse, D. J.; Johnsen, S. N. (2011). "A Chiton Uses Aragonite Lenses to Form Images". Current Biology 21 (8): 665–670.
^ a b c Wilson, M. (1978). "The functional organisation of locust ocelli". Journal of Comparative Physiology 124 (4): 297–316.
^ Wagner, H.J., Douglas, R.H., Frank, T.M., Roberts, N.W., and Partridge, J.C. (Jan 27, 2009). "A Novel Vertebrate Eye Using Both Refractive and Reflective Optics". Current Biology 19 (2): 108–114.
^ Völkel, R; Eisner, M and Weible, K. J (June 2003). "Miniaturized imaging systems" (PDF). Microelectronic Engineering. 67–68 (1): 461–472.
^ Land, Michael (1997). "Visual Acuity in Insects" (PDF). Annual Reviews Entomology 42: 147–77.
^ Gaten, Edward (1998). "Optics and phylogeny: is there an insight? The evolution of superposition eyes in the Decapoda (Crustacea)". Contributions to Zoology 67 (4): 223–236.
^ Ritchie, Alexander (1985). "Ainiktozoon loganense Scourfield, a protochordate? from the Silurian of Scotland". Alcheringa 9 (2): 137.
^ Mayer, G. (2006). "Structure and development of onychophoran eyes: What is the ancestral visual organ in arthropods?". Arthropod Structure and Development 35 (4): 231–245.
^ Greiner, Birgit (16 December 2005). Adaptations for nocturnal vision in insect apposition eyes (PDF) (Ph.D.). Lund University. Retrieved 13 November 2014.
^ a b Jochen Zeil & Maha M. Al-Mutairi (1996). "Uca lactea annulipes"Variations in the optical properties of the compound eyes of (
^ Ullrich-Luter, E. M.; Dupont, S.; Arboleda, E.; Hausen, H.; Arnone, M. I. (2011). "Unique system of photoreceptors in sea urchin tube feet". Proceedings of the National Academy of Sciences 108 (20): 8367–8372.
^ Ali & Klyne 1985, p. 8
^ a b c d e f Land, M. F. (1989). "The eyes of hyperiid amphipods: relations of optical structure to depth". Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology 164 (6): 751–762.
^ Ali & Klyne 1985, p. 28
^ Russ, John C. (2006). The Image Processing Handbook. CRC Press.
^ Klaassen, Curtis D. (2001). Casarett and Doull's Toxicology: The Basic Science of Poisons. McGraw-Hill Professional.
^ The Retina
^ Fischer, Robert E.; Tadic-Galeb, Biljana and Plympton, Rick (2000). Steve Chapman, ed. Optical System Design. McGraw-Hill Professional.
^ Barlow, H. B. (1952). "The size of ommatidia in apposition eyes" (PDF). J Exp Biol 29 (4): 667–674.
^ Ali & Klyne 1985, p. 161
^ Barlow, Horace Basil and Mollon, J. D (1982). The Senses. Cambridge: Cambridge University Press. p. 98.
^ Fernald, Russell D. (1997). "The Evolution of Eyes" (PDF). Brain, Behaviour and Evolution 50 (4): 253–259.
^ a b c d e Goldsmith, T. H. (1990). "Optimization, Constraint, and History in the Evolution of Eyes".
^ a b c d e f Nilsson, E.; Arendt, D. (Dec 2008). "Eye Evolution: the Blurry Beginning". Current Biology 18 (23): R1096–R1098.
^ There is no universal consensus on the precise total number of phyla Animalia; the stated figure varies slightly from author to author.
Adaptation (eye) (Night vision)
Arthropod eye
Cephalopod eye
Emission theory (vision)
Eye movement (sensory)
Mammalian eye
Mollusc eye
Nictitating membrane
Simple eye in invertebrates
Eye development
The structures of the eye labeled
Another view of the eye and the structures of the eye labeled
There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells, and r-opsins, associated with rhabdomeric photoreceptor cells.[45] The eyes of vertebrates usually contain cilliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that remnants survive in the eyes.[45] Likewise, c-opsins have been found to be expressed in the brain of some invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form.[45] C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins.[45] Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins – but r-opsins are yet to be found in this group.[45] Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment.[45]
Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the photoreceptor cells from light leaking in from the sides. The opsin protein group evolved long before the last common ancestor of animals, and has continued to diversify since.[2]
The pigment molecules used in the eye are various, but can be used to define the evolutionary distance between different groups, and can also be an aid in determining which are closely related – although problems of convergence do exist.[44]
Cones are responsible for color vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, they connect through adjoining cells within the retina to send an electrical signal to the optic nerve fibres. The optic nerves send off impulses through these fibres to the brain.[44]
Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision; they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.
The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones.
Rods and cones
Most organisms with colour vision are able to detect ultraviolet light. This high energy light can be damaging to receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets in the course of evolution, is to make the lens impervious to UV light — this precludes the possibility of any UV light being detected, as it does not even reach the retina.[44]
[2] The most sensitive pigment,
"Color vision is the faculty of the organism to distinguish lights of different spectral qualities."[41] All organisms are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly between wavelengths of 400 and 700 nm.[42] This is a rather small section of the electromagnetic spectrum, probably reflecting the submarine evolution of the organ: water blocks out all but two small windows of the EM spectrum, and there has been no evolutionary pressure among land animals to broaden this range.[43]
Perception of colors
However, in the compound eye, the resolution is related to the size of individual ommatidia and the distance between neighbouring ommatidia. Physically these cannot be reduced in size to achieve the acuity seen with single lensed eyes as in mammals. Compound eyes have a much lower acuity than vertebrate eyes.[40]
Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair.[39] A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.
For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD[36] (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD.[37] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye's central fovea region.[38]
Visual acuity, or resolving power, is "the ability to distinguish fine detail" and is the property of cone cells.[35] It is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white/black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a grey block, is then the measurement of visual acuity of the eye.
The eye of a red-tailed hawk
Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organism's carapace; this also allows them to track predators or prey without moving the head.[9]
It is not only the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms, and this can act as a pressure on organisms to have more transparent eyes at the cost of function.[34]
Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential mates against a very large backdrop.[34] On the other hand, the eyes of organisms which operate in low light levels, such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be captured.[34]
An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey.[34] In deep water organisms, it may not be the centre of the eye that is enlarged. The [34] Depth perception can be enhanced by having eyes which are enlarged in one direction; distorting the eye slightly allows the distance to the object to be estimated with a high degree of accuracy.[9]
Of course, for most eye types, it is impossible to diverge from a spherical form, so only the density of optical receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that reflects the region of highest data acquisition.[1]:23–4 Optical superposition eyes are constrained to a spherical shape, but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon, without altering the size or density of individual ommatidia.[34] Eyes of horizon-scanning organisms have stalks so they can be easily aligned to the horizon when this is inclined, for example if the animal is on a slope.[31]
Eyes are generally adapted to the environment and life requirements of the organism which bears them. For instance, the distribution of photoreceptors tends to match the area in which the highest acuity is required, with horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of ganglia, with acuity decreasing outwards from the centre.
Relationship to life requirements
The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye.[33] It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid), no blood vessels, and 98–99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibres with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye.
The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator muscle.
The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons. The tube feet of sea urchins contain photoreceptor proteins, which together act as a compound eye; they lack screening pigments, but can detect the directionality of light by the shadow cast by its opaque body.[32]
Another version is the pseudofaceted eye, as seen in Scutigera. This type of eye consists of a cluster of numerous ocelli on each side of the head, organised in a way that resembles a true compound eye.
There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye.
Good fliers such as flies or honey bees, or prey-catching insects such as fovea area which gives acute vision. In the acute zone the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil. This occurs because the ommatidia which one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it.[31]
Another kind of compound eye, found in Strepsiptera, employs a series of simple eyes—eyes having one opening that provides light for an entire image-forming retina. Several of these eyelets together form the strepsipteran compound eye, which is akin to the 'schizochroal' compound eye some trilobites had. Because each eyelet is a simple eye, it produces an inverted image; those images are combined in the brain to form one unified image. Because the aperture of an eyelet is larger than the facets of a compound eye, this arrangement allows vision under low light levels.[1]
This eye type functions by refracting light, then using a parabolic mirror to focus the image; it combines features of superposition and apposition eyes.[9]
Parabolic superposition
The second type is named the superposition eye. The superposition eye is divided into three types; the refracting, the reflecting and the parabolic superposition eye. The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye is normally found in nocturnal insects because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution.[30] In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses.
Superposition eyes
Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium.
Apposition eyes are the most common form of eyes, and are presumably the ancestral form of compound eyes. They are found in all arthropod groups, although they may have evolved more than once within this phylum.[1] Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point.[1] (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.)
Apposition eyes
Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image.[27] Compound eyes are common in arthropods, and are also present in annelids and some bivalved molluscs.[28] Compound eyes, in arthropods at least, grow at their margins by the addition of new ommatidia.[29]
A compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light.[25] Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained (assuming that they do not function as phased arrays). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require very large compound eyes, around 11 m in radius.[26]
Arthropods such as this Calliphora vomitoria fly have compound eyes
Anatomy of the compound eye of an insect
An image of a house fly compound eye surface by using scanning electron microscope
There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals.[24]
Many small organisms such as Pecten has up to 100 millimetre-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses.[1]
An alternative to a lens is to line the inside of the eye with "mirrors", and reflect the image to focus at a central point.[1] The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out.[1]
Reflector eyes
As mentioned above, a refractive cornea is only useful out of water; in water, there is little difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the water – penguins and seals, for example – lose their highly curved cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strongly focusing cornea.[1]
In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air.[1] In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas, the lens tissue is corrected with inhomogeneous lens material (see Luneburg lens), or with an aspheric shape.[1] Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view often have eyes that make use of an inhomogeneous lens.[1]
Refractive cornea
Some marine organisms bear more than one lens; for instance the copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilia, has two lenses in each eye, arranged like those in a telescope.[1] Such arrangements are rare and poorly understood, but represent an alternative construction. Multiple lenses are seen in some hunters such as eagles and jumping spiders, which have a refractive cornea (discussed next): these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.[1]
Multiple lenses
The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently they can never form a sharp image. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain.[23] Focusing the image would also cause the sun's image to be focused on a few receptors, with the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity.[23] This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above).[23]
This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimise the effect of eye motion while the animal moves, most such eyes have stabilising eye muscles.[1]
Heterogeneous eyes have evolved at least nine times: four or more times in [1]
The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable.[1] The most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina.[1] This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration.[1] Such an inhomogeneous lens is necessary in order for the focal length to drop from about 4 times the lens radius, to 2.5 radii.[1]
Spherical lensed eye
Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates.
[1] The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.[1] Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eye". They are small, comprising up to about 100 cells covering about 100 µm.[1]
Cranial nerves, Optic tract, Oculomotor nerve, Trigeminal nerve, Vestibulocochlear nerve
Optic nerve, Pupil, Retina, Cornea, Iris (anatomy)
Vision in fishes
Digital object identifier, FishBase, Eye, Fish, Camouflage
Parietal eye
Eye, Evolution, Cerebellum, Diencephalon, Optic nerve
Eye, Horse, Color, Evolution, Latin


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