 Why was the large Kallerian not chosen for the journey?
It was our first day of recruiting on the planet, and the alien life-forms had lined up for hundreds of feet back from my rented office. My three staff men, Auchinleck, Stebbins and Ludlow, walked shieldwise in front of me. The aliens came in every shape and form, in all colors and textures—and all of them eager for a Corrigan contract. There was a lidless eye at the top of his head and five lidded ones, one above each arm. "Before we begin, I'll need certain information about—" "I am a being of Regulus II," came the grave, booming reply, even before I had picked up the blank. The being closed his eyes and toddled around in a 360-degree rotation, remaining in place. I'll be required to remain on exhibit no more than one-third of each Terran sidereal day." We needed a green Regulan in our show; the last one had quit four years ago. But just because we needed him didn't mean we had to be extravagant in hiring him. A Terraphile alien who goes to the extent of rechristening himself with a Terran monicker would work for nothing, or even pay us, just so long as we let him get to Earth. He was followed by a roly-poly blue-skinned humanoid from Donovan's Planet, four feet high and five hundred pounds heavy. We already had a couple of his species in the show, but they made good crowd-pleasers, being so plump and cheerful. I passed him along to Auchinleck to sign at anything short of top rate. It was the isolationism of the late 29th century that turned me into the successful proprietor of Corrigan's Institute, after some years as an impoverished carnival man in the Betelgeuse system. Before then, anyone could visit Earth. After the gate clanged down, a non-terrestrial could only get onto Sol III as a specimen in a scientific collection—in short, as an exhibit in a zoo. At the same time, we had turned away a dozen ursinoids, fifty of the reptilian natives of Ghryne, seven Sirian spiders, and no less than nineteen chlorine-breathing Procyonites wearing gas masks. It was also my sad duty to nix a Vegan who was negotiating through a Ghrynian agent. So far as I could tell, the being was quite plainly nothing but an Earthman. "I happen to be a representative of the only Earthlike race that exists anywhere in the Galaxy but on Earth itself.
 There were already four Kallerians in inventory.
 There were already four Kallerians in inventory.  His species was too large to travel in the group.  He was argumentative during the interview process.  His payout demands  exceeded their budget.