Name the primary and secondary lymphoid organs.

(N/A) Primary lymphoid organs are the sites where lymphocytes originate and/or mature and become antigen-sensitive. These include the $Bone \, marrow$ and the $Thymus$.
Secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells. These include the $Spleen$, $Lymph \, nodes$, $Tonsils$, $Peyer's \, patches$ of the small intestine, and $Appendix$.