title: Crisis of identity.
mesh_terms: D000486:Allergy and Immunology; D000663:Amphibians; D000717:Anatomy, Comparative; D000818:Animals; D000917:Antibody Formation; D006084:Graft Rejection; D007108:Immune Tolerance; D008213:Lymphocyte Activation; D010163:Paleontology; D010802:Phylogeny