2004). B-lymphocytes, the cells that produce antibodies, are initially produced in the embryonic liver, yolk sac and bone marrow, then move through the blood to the bursa of Fabricius (BF). Birds have a bursa of Fabricius (BF), which is an outpocketing of cloaca.
Most squirrels are vegetarians. There are a few exceptions like the flying squirrel. The flying squirrel will eat small birds, insects and definitely steal eggs from birds nest in order to make a meal. Generally speaking though, squirrels will mainly stick to things that are vegetarian related.
Northern and southern flying squirrels are the smallest of the tree squirrels and the only nocturnal species. They are also known to be the most carnivorous of the group, feeding primarily on nuts and seeds, but also on insects and bird eggs. These squirrels feed on nuts, acorns seeds, berries, some insects and bird eggs.