68 ME. SWALE VINCENT ON THE 



2. The interrenal, in its histological features, very closely resembles the suprarenals 

 of Teleosts, and in some cases its structure is almost identical with that of the cortex 

 of certain Mammalian capsules. 



3. The paired bodies, as we have seen, have not such a definitely glandular 

 appearance. They consist simply of a fibrous stroma, protoplasm, nuclei of various- 

 characters l , and nervous elements. 



Although the question is still very doubtful, and though I have not attempted any 

 investigation of the development, I am decidedly inclined to the view that if one and 

 not both of these bodies corresponds to the suprarenals of the higher Vertebrata, this 

 one is the interrenal and not the paired suprarenal. And I am led to this view from 

 consideration of its general appearance and position as well as its minute structure 2 . 



I think there can no longer be any doubt, at all events, that the paired suprarenals 

 and the interrenals are totally distinct structures and almost certainly have quite 

 different functions. 



On the other hand, one is much more tempted to believe that the interrenal 

 corresponds to the cortex and the paired suprarenals to the medulla of the Mammalian 

 capsules, and this hypothesis would, so far as I can see, accord fairly well with known 

 facts. But I should hesitate to give myself over entirely to this view until the 

 development of the suprarenals in Mammals has been put upon a more satisfactory 

 basis. Besides, even if this hypothesis were correct, it would not be by any means a 

 final solution of the difficulty. For the questions naturally arise, What is the 

 significance of this dual origin in Elasmobranchs'? What is the essential nature 

 of the interrenal and the segmental bodies 1 Balfour and others have proved 

 conclusively a very intimate structural and developmental connection between the 

 sympathetic chain and the segmental bodies. But, in effect, what does this mean? 

 The segmental bodies are not in their essence nervous structures, and we know of 

 nothing elsewhere which illustrates or throws any light on this curious development 

 of glandular material in connection with the nervous system. 



Again, I am not sure that the paired segmental bodies are not more intimately related 

 to the blood-vascular than to the nervous system. We have seen that each one is 

 placed around an arteriole, and many of them are immersed in the blood of the cardinal 

 sinus. Further, it occurs to me that, after all, their connection with the sympathetic 

 system may be in a certain sense accidental : i. e. they are abundantly supplied by the 

 sympathetic as are other abdominal organs ; but that, owing to their position, close to 



1 See footnote 2, page 66. 



• Since the above was written, and as the result of further investigations throughout Vertebrates, I have 

 elsewhere emphasized the view that the suprarenals of Mammals are to he regarded as compound glands derived 

 from these two organs in Elasmobranch Fishes, and have suggested that each portion probably has a distinct 

 function. The function of the medulla is becoming tolerably well understood. The function of the cortex is 

 still unknown (Oliver and Schafer, Proc. Physiological Society, 1895 ; Swale Vincent, Proc. Birm. Nat. Hist. & 

 Phil. Soc. 1896, vol. s. pt. i. ; Birm. Med. B,eview, Aug. 1896 ; also Anat, Anz. xiii. Bd. Nr. 1 & 2, 1897). 



