74 ALBERT KTTNTZ 



substance are derived from the sympathetic nervous system, in 

 his opinion, requires further proof. 



Aichel ('00) advanced a new theory of the origin of the adrenals. 

 According to this author, the interrenals alone in the selachians 

 are homologous with the adrenals of the higher vertebrates. 

 These, he believes, arise from the peritoneal invaginations of the 

 pronephros. The so-called suprarenals in the selachians, he con- 

 cludes, are derived from retrograding canals of the same body. 

 In embryos of both the rabbit and the mole, according to Aichel, 

 both the cortical and the chromaffin substance are derived from 

 the epithelium of the pronephros. This view finds no support 

 in the work of other investigators. 



Wiesel ('01), although his observations were made on embryos 

 of the pig which were too far advanced to reveal the earliest traces 

 of the adrenal anlagen, concluded that the cortical substance is 

 derived from the peritoneal epithelium, while the chromaffin sub- 

 stance is derived from the prevertebral sympathetic plexuses. 



Whitehead ('03) studied the development of the adrenals in 

 embryos of the pig from their earliest anlagen. His conclusions 

 agree in general with the conclusions of Wiesel above cited. 



By an exhaustive review of the literature and by extensive ob- 

 servations, Poll ('06) has shown that the weight of evidence is 

 in favor of the view that in all the classes of vertebrates the cor- 

 tical substance of the adrenals arises from the peritoneal epithe- 

 lium, while the chromaffin substance is derived from cells which 

 become separated from the anlagen of the sympathetic nervous 

 system. The genetic relationships of the cells which give rise 

 to the chromaffin substance, however, as well as the processes 

 by which these cells become associated with and approximated to 

 the cortical substance and by which they become transformed into 

 typical chromaffin cells have not been understood. 



During my studies of .the development of the sympathetic 

 nervous system in embryos of the Loggerhead turtle (Thalas- 

 sochelys caretta), my attention was attracted by the phenomena 

 involved in the development of the adrenals. Embryos of this 

 species afford excellent material for the study of these phenomena 

 because the chromaffin material is comparatively abundant, the 



