Observations on the fat‐body in Hymenoptera

An histological and cytological study of the postembryonic history of the fat‐body in Pteronidea ribesi (Scopoli) and Diphadnus appendiculata (Hartig) (both Tenthredinidae) and in Macrocentrus ancylivora Rohwer (Ichneumonidae). The two principal components of the fat‐body are the urate‐storing excretory cells and the fat‐cells. The development and behavior of the excretory cells, especially during the metamorphosis, are described, and in Pteronidea their origin is traced to leucocytes which have become associated with the fat‐cells. In the albuminoid inclusions found in the fat‐cells two types of substance are distinguished: ( a ) a basophile material, of nuclear origin, which appears only during the metamorphosis; ( b ) an acidophile material which appears already during the early larval stages in Macrocentrus, but in Pteronidea is formed only during the metamorphosis and in association with the basophile material. It is thus found that albuminoids formed slowly during larval life may exist from the beginning in the form of acidophile spheres, as occurs in Macrocentrus. But those formed rapidly during the metamorphosis, in all the forms studied, are formed in association with a basophile material derived from the nucleus. The significance of intracellular changes during the metamorphosis is discussed, and the final disposition of the cell inclusions as well as of the fat‐cells themselves is described.