The Comparative Histology of the Suprarenal Capsules. 315 



XI. Summary and Conclusions. 



1. The Suprarenal capsule in Vertebrates is made up of two 

 separate and distinct glands — the cortex and the medulla. In 

 Elasmobrancli Fishes these two are quite independent. In Amphibia 

 and Eeptilia the medulla is placed close to the cortex but only to a 

 comparatively small extent mixed up with it. In Birds the two are 

 irregularly combined, while in Mammals the medulla occupies a position 

 in the centre of the cortical substance. 



2. Far from heing in any sense "rudimentary organs^', the tivo 

 constituents of the suprarenal capsule show a progressive development 

 as tue ascend the Vertebrate scale, the mediala especially becoming 

 more and more glandular in structure as tue reach the Mammalia. 



3. Developmental researches show that the medulla is derived 

 from the nerve-cells of the sympathetic ganglia. This origin is revealed 

 also by the histological structure in the adult in Elasmobranchs, Am- 

 phibians, Reptiles, and Birds, where transition forms are found 

 bettveen nerve-ganglion cells and the proper cells of the medullary 

 substance. 



4. According to the best evidence the cortex in Mammals is 

 derived from the germ epithelium. 



5. Although the medullary gland is nervous in origin, in the 

 adult it seems to be no longer nervous but glandular, having a 

 characteristic internal secretion. 



6. The medulla of the suprarenal capsule in the higher Verte- 

 brates corresponds to the paired suprarenal bodies along the sym- 

 pathetic in Elasmobrancli Fishes. This is shewn by physiological 

 means, i. e. these paired bodies contain the same active principle as 

 the medulla of the suprarenal capsule in higher Vertebrates, and also 



teresting to note that certain cells are described in connection with the abdominal 

 sympathetic ganglia which are not nerve-cells and closely resemble the medullary 

 suprarenal cells. Kohn [68] states that these become stained browii with potassium 

 bichromate. 



With regard to the paired bodies anterior and posterior to these, it is not 

 impossible that they may be represented in the Mammalia by such glands as the 

 "carotid" and the "coccygeal". I would rather throw this out as a suggestion 

 than hazard it as an opinion. 



