xii INTERNAL SECRETION AND DUCTLESS GLANDS 225 



structure in the adult shows no resemblance to that of the 

 organs described above. 



Another epithelial derivative, but one having a quite dif- 

 ferent structure from the rest, is the post branchial body, a 

 paired organ lying beneath the mucus membrane of the 

 pharynx on either side of the glottis. Each organ, accord- 

 ing to Maurer, consists of a group of four to six small folli- 

 cles, lined by cylindrical epithelium, which sometimes bears 

 cilia. Its structure resembles that of the thyroid glands, 

 but the follicles contain a thin fluid instead of a colloidal 

 substance (Maurer). 



A small lymphoid organ, the procoracoidal body, has 

 recently been discovered by Gaupp between the coracoid 

 and procoracoid portions of the pectoral girdle. Its mode 

 of origin has not been traced, but it is found in young larvae 

 with external gills. It probably does not belong in the 

 category of epithelial bodies, although it bears a certain 

 resemblance to them in internal structure. 



The Adrenal Bodies. — The adrenal bodies are thin bands 

 of a golden yellow color extending along the middle of the 

 ventral surface of the kidneys. They consist essentially of 

 small solid groups of cells which lie close to the branches of 

 the renal veins. Among the ordinary epithelial cells com- 

 posing the main bulk of the organs are scattered cells of 

 larger size and often of brownish color. The former, accord- 

 ing to Stilling, correspond to the peripheral or cortical cells of 

 the adrenals of mammals, and the latter to the central cells. 

 A third type of cell, which is characterized by its granular 

 contents, and its taking an intense red color when stained in 

 eosin, was found by Stilling to occur only during the summer 

 months. On the other hand, the ventral portion of the 

 adrenals was found to contain numerous lymphoid cells only 

 in the winter and spring. The " cortical cells " are derived 

 Q 



