Histological studies on the lymphoid organs in prenatal larvae of platy, Xiphophorus maculatus L. (Poeciliidae: Teleostei)

The thymus was very large and tightly packed by lymphocytes in prenatal larvae of platy, Xiphophorus maculatus L., whereas the lymphoid tissues in the spleen and trunk kidney were poorly developed at these stages. We therefore suggest that the specific cellular defence is developed much earlier than the corresponding humoral defence mechanisms in this species.