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.
Pine squirrels (Tamiasciurus), like Douglas and American red squirrels, are larder hoarders who eat primarily tree seeds (pine cones); as well as other foods that they can find such as mushrooms, buds, catkins, flowers and berries, storing all of their food in a single location or midden (larder).