DEVELOPMENT OF THE ADRENALS IN THE TURTLE /5 



embryos are comparatively large, develop comparatively slowly 

 and afford excellent histological preparations. 



The development of the adrenals has been investigated less 

 extensively in the Reptilia than in the other classes of vertebrates. 

 Our limited knowledge of the development of these organs in this 

 class of vertebrates is the more appreciable because the adrenals 

 in this, the most primitive class of the Amniota represent a tran- 

 sition stage in the evolution of the highly specialized adrenal organs 

 in the higher vertebrates from the more primitive adrenal system 

 in the Anamnia. 



Observations which have been recorded on the development of 

 the adrenals in the Crocodilia and the Ophidia are only frag- 

 mentary and inconclusive. More or less extensive observations 

 on the development of these organs in the Sauria, primarily in 

 certain species of the genus Lacerta, have been recorded by 

 Braun (79, '82), von Mihalcovics ('85), Weldon ('85), Hoffmann 

 ('89) and Soulie ('03). von Mihalcovics, being an advocate of 

 the theory of the homogeneous origin of the adrenals, derived 

 both the cortical and the chromaffin substance from the germinal 

 epithelium. The other investigators above mentioned agree in 

 deriving the chromaffin substance from the anlagen of the pre- 

 vertebral sympathetic plexuses. They do not agree, however, 

 as to the origin of the cortical substance. According to Braun, 

 the cortical substance arises directly from the mesenchyme. Ac- 

 cording to Weldon and Hoffmann, it arises from the epithelium 

 of the pronephros. According to Soulie, it arises from the per- 

 itoneal epithelium. 



The only extended observations on the development of the 

 adrenals in the Chelonia which have been recorded, as far as the 

 writer is aware, are those of Poll ('04, '06) on embryos of Emys 

 europaea. This author describes the origin of the cortical sub- 

 stance from the peritoneal epithelium in detail. He has little 

 to say, however, concerning the chromaffin substance except 

 that it is derived from the anlagen of the prevertebral sympathetic 

 plexuses. 



The following observations are based almost exclusively on 

 embryos of the Loggerhead turtle (Thalassochelys caretta) . 



