THE LATER DEVELOPMENT OF THE FROG 



207 



beneath the peritoneal epithelium from which they appear to 

 have arisen. Just after metamorphosis these cell groups 

 separate from the peritoneum, and begin to send out branching 

 and anastomosing processes which soon form a network, like 

 that of the cortical substance of the adult. 



The medullary or phseochrome substance is derived originally 

 from ganglia of the sympathetic nervous system. After the 

 central network is established there appear within the sym- 

 pathetic ganglia of the mesonephric region groups of cells, the 

 precise origin of which is not clear, having the properties of 



ct 



FIG. 78. Parts of sections through young R. temporaria, showing the origin 

 of the adrenal bodies. After Srdinko. A. Through 30 mm. tadpole. B. 

 Through 11 mm. frog after metamorphosis, a, Dorsal aorta; ac, cortical cells 

 of adrenal body; am, medullary cells of adrenal body; ct, connective tissue; 

 fir, gonad; 0s, sympathetic ganglion; m, mesentery; n, mesonephros; rv, revehent 

 renal vein^ v, vena cava; x, point where ganglion cells enter mesonephros and 

 adrenal body. 



iese phseochrome cells. Some of these cell groups remain 

 the 'sympathetic ganglia, while others appear to migrate into 

 the rudiment of the adrenal body, where they become scattered 

 through the cortical tissue (Fig. 78, B). The method by which 

 they extend into the adrenal is not clearly known in the frog. 



VII. THE SKELETON AND TEETH 



In describing the development of the skeletal system we 

 shall limit our account to the establishment of the essential 



