Haemal nodes are lymphoid organs found in various mammals and some birds.

The peripheral lymphoid organs are the sites of lymphocyte activation by antigen.

At this point the T cells leave the primary lymphoid organ and enter the blood stream.

The lymphoid organ might display spheroids, but is otherwise unremarkable.

Macrophage heterogeneity is indeed quite common, even within a single lymphoid organ.

They then populate the lymphoid organs for storage until needed.

The bursa is an epithelial and lymphoid organ that is found only in birds.

Once in a secondary lymphoid organ the B cell can be introduced to an antigen that it is able to recognize.

In the bone marrow (the central lymphoid organ), central tolerance is produced.

There is also poor development of the secondary lymphoid organs.