Summary

The structure of the adrenal tissue was investigated by both histological and histo-chemical techniques. It is shown that the adrenal contains 4 types of tissues; these are named the steroid, Stilling, lymphoid, and chromaffin tissues. The structure of the adrenal in the bullfrog does not provide any evidence to support a theory of zonation within the cortical tissue of the Anura, as suggested by some authors. There is no alteration in the appearance or numbers of the 'summer cells ' of Stilling that can be correlated with the time of year or with the sexual activity of the animal. For this reason it is considered preferable to call these 'Stilling cells', as was suggested byMagath(igi5). There is evidence that structural differences are to be found between the Stilling cells and the granulocytes found in the lymphoid tissue