There were initially supposed to be just two pet pill bugs on Terror. Neptune (Crozier's) and Reuben (Little's). They were free-roaming, but that shouldn't be an issue, since they're both male...
Turns out Reuben is female and Edward just didn't know what to look for, since it's his first ever pill bug and nobody else was brave enough to lift up a lieutenant's pet.
One day Edward simply flips him her over to scratch her belly and finds an egg pouch on her underside.
Crozier is obviously angry when he finds out - they're going to have a bloody pill bug invasion on the ship! HOW did Edward not know what a female pill bug looked like?! But when he gets over the initial anger, he's ultimately too soft to actually get rid of the eggs and lets Edward keep them.
When they're hatched, Reuben doesn't let anyone near the little ones except Edward and Jopson, for some reason, so they help take care of them and keep them contained so they don't get stepped on - they're very tiny. Mouse sized.
When they're weaned and have gained their colour and a bit of size, Edward decides to hand them out.
Sir John has one of his own already, so he politely declines. He gives one to Fitzjames, who (to Edward's disdain) names it Gaius Marius. Le Vesconte says he'll be helping Fitzjames with the care, so doesn't want one. Hodgson takes two and names them Corinna and Anyte. Gore takes one with joy - he's wanted one for years, but never got around to it. After a lot of thinking about the name, he simply gives up and names it first thing that comes to mind - Clifford.
The marines get one. They can't decide on a name, but they're calling him Private Scuttle for now. Goodsir takes two, names one Pulchra and intends to give the other to Stanley, but he's nervous and keeps postponing it. Collins takes one, but cautiously, since he got bitten by one when he was a child, but gosh, this one is very cute... Edward also keeps one for himself.
Blanky, Irving, Jopson, Bridgens and McDonald all decline the offer. (McDonald is especially saddened to decline, since they're "quite charming little creatures" but he simply doesn't have the time)
When nobody else comes to mind he gives one to Tom Hartnell, who - upon learning it's a she - names her Jane.
Edward does regular check ups after they've all been handed out to make sure they're okay.
Two weeks later and Goodsir suddenly has just Pulchra. "Where did the other one go?" "Oh, Dr. Stanley has accepted my offer. He seems to like the little creature after all." *cut to Stanley napping with his new best friend curled up beside him*
