DEVELOPMENT OF THE ADRENALS IN THE TURTLE 77 



At the close of the eighth day of incubation, the buds in the 

 middle region of the adrenal zone rise in the mesenchyme as high 

 as the middle level of the aorta and in sections occupy the greater 

 part of the area between the aorta and the mesonephros (fig. 2, 

 ad). The cells in these buds are now arranged in more or less 

 regular rows rising from the base of the wedge-shaped aggregate 

 toward its apex which is usually slightly recurved toward the 

 mesial surface of the mesonephros. Mitotic figures may occasion- 

 ally be observed in these growing buds. It is obvious, therefore, 

 that these cells retain the power of further propagation by division 

 after they have advanced into the adrenal anlagen, thus giving 

 the latter the capacity of independent growth after they are no 

 longer connected with the peritoneal epithelium. 



As development advances, the adrenal buds become larger and 

 advance farther into the mesenchyme, rarely, however, rising but 

 slightly higher than the middle level of the aorta. They no 

 longer appear wedge-shaped in transverse sections, but have be- 

 come rounded or oval in outline, retaining connection with the 

 peritoneal epithelium only by a slender stalk (fig. 3, ad). During 

 the tenth day of incubation, some of the buds become almost or 

 completely separated from the peritoneal epithelium. They now 

 appear in transverse sections as condensations in the mesenchyme 

 between the aorta and the mesonephros and are often so closely 

 approximated to the mesial surface of the latter that except for 

 a slight difference in the staining properties of the cells compos- 

 ing them it becomes difficult to distinguish between these two 

 complexes. Such conditions, doubtless, are responsible for the 

 conclusions of some of the earlier investigators that the cortical 

 substance of the adrenals is derived either directly from the 

 mesenchyme or from the epithelium of the mesonephros. 



At the close of the eleventh day of incubation, the adrenal an- 

 lagen have become separated from the peritoneal epithelium 

 throughout nearly the entire extent of the adrenal zone. In 

 transverse sections, they appear more or less circular in outline, 

 being modified in form somewhat by the limitations of the area 

 between the aorta and the mesonephros (fig. 4, ad). In the ante- 

 rior and the middle region of the adrenal zone, the adrenal anlagen 



