The lymphoid system.
D000818:Animals; D005075:Biological Evolution; D002060:Bursa of Fabricius / Q000601:surgery; D007153:Immunologic Deficiency Syndromes; D008198:Lymph Nodes / Q000276:immunology; D008208:Lymphatic System / Q000254:growth & development; D008214:Lymphocytes; D008221:Lymphoid Tissue / Q000166:cytology