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.
Bird enthusiasts aren't nuts for squirrels, but many others welcome these furry critters in their backyard. If you want to lure squirrels with nuts, you'll likely have success, as they'll happily eat nothing but nuts. However, squirrels need other nutrients nuts can't provide, so other foods are welcome. Fruits and vegetables, such as apples, lettuce, carrots, grapes, squash, watermelon, cherries, celery, and broccoli are fine additions to a squirrel's diet.