DEVELOPMENT OF ELASMOBKANCH FISHES. 245 



Leydig's description \ They are rather granular in appearance, 

 and are mainly peculiar from the somewhat large size of the 

 nucleus. The diameter of an average cell is about '015 Mm., 

 and that of the nucleus about '01 to "012. The nuclei are 

 remarkably granular. The septa of the body are provided with 

 a fairly rich capillary network. 



At the first glance there is some resemblance in struc- 

 ture between the tissues of the suprarenal and interrenal 

 bodies, but on a closer inspection this resemblance resolves 

 itself into both bodies being divided up into lobules by 

 connective-tissue septa. There is in the interrenal body no 

 distinction between cortical and medullary layers as in the 

 suprarenal. The cells of the two bodies have very different 

 characters, as is demonstrated by a comparison of the rela- 

 tive diameters of the nuclei and the cells. The cells of the 

 suprarenal bodies are considerably larger than those of the 

 interrenal ('021 to '03 as compared to '015), yet the nuclei 

 of the larger cells of the former body do not equal in size 

 those of the smaller cells of the latter ("009 as compared to 

 •01). 



My observations both on the coarser anatomy and on the 

 histology of the interrenal body in the adult point to its 

 being in no way connected with the suprarenal bodies, 

 and are thus in accordance with the earlier and not the 

 later views of Leydig. 



The embryology of this body (under the title of suprarenal 

 body) was first described in my preliminary account of the 

 development of the Elasmobranch Fishes ^ A short account 

 of its embryonic structure was given, and I stated that although 

 I had not fully proved the point, yet I believed it to be 

 derived from the wall of the alimentary canal. As will be 

 shewn in the sequel this belief was ill-founded, and the organ 

 in question is derived from the mesoblast. Allusion has also 

 been made to it by Professor Semper, who figures it at an 

 early stage of development, and implies that it arises in the 



1 Perhaps the body I am describing is not identical with Leydig's posterior 

 suprarenal body. I do not, as mentioned above, feel satisfied that it is so from 

 Leydig's description. 



^ Quarterly Journal of Microscopic Science, October, 1874. 



