80 ALBERT KUNTZ 



the cortical substance. The chromaffin substance arises in an 

 entirely different manner. As has been repeatedly maintained 

 by certain investigators and denied by others, for the several 

 classes of vertebrates, and as has been shown by Poll also for the 

 turtle (Emys europaea), this part of the adrenal system is derived 

 from the anlagen of the prevertebral sympathetic plexuses. It 

 is, therefore, primarily of ectodermal origin. 



During the eighth day of incubation, when the adrenal buds 

 appear as small cell-aggregates arising from the peritoneal epi- 

 thelium, the anlagen of the ganglia of the sympathetic trunks are 

 already present as irregular cell-groups lying in the mesenchyme 

 approximately at the dorsal level of the aorta (fig. 1, sy). As 

 development advances, the anlagen of the sympathetic trunks 

 become larger and, as the writer has shown in an earlier paper 

 ('11 a), cells become separated from them and migrating ventrally 

 give rise to the anlagen of the prevertebral sympathetic plexuses 

 which are located along the ventro-lateral aspects of the aorta. 



During the eleventh day of incubation, sympathetic elements 

 may be traced ventrally from the anlagen of the sympathetic 

 trunks along the lateral surfaces of the aorta. In the anterior 

 and the middle region of the adrenal zone where the adrenal an- 

 lage is still located between the mesonephros and the aorta, sym- 

 pathetic cells may in some sections be observed in contact with 

 the anlage of the cortical substance, but no such elements could 

 be observed, at this stage, among the cortical cells (fig. 4, syc) . 



At the close of the thirteenth day of incubation, sympathetic 

 cells may be observed as far ventrally as the ventral level of the 

 aorta and the anlagen of the prevertebral sympathetic plexuses 

 have become well established. The adrenal anlagen now lie in 

 close proximity with the anlagen of the prevertebral sympathetic 

 plexuses and in some sections small groups of sympathetic cells 

 may be observed in contact with the cortical mass (fig. 5). 



As development advances, the cells composing the anlagen of 

 the prevertebral sympathetic plexuses become more numerous 

 until at the close of the nineteenth day of incubation the aorta is 

 completely encircled ventrally by conspicuous aggregates of sym- 

 pathetic cells (fig. 6, pv) . The adrenal anlagen are now somewhat 



