DEVELOPMENT OF ELASMOBHAXCH FISHES. 243 



definite lumen, and take a course through the centre of these 

 bodies, as do the aortic branches in the adult. 



By stage O these bodies have acquired a distinct mesoblastic 

 investment, which penetrates into their interior, and divides it, 

 especially in the case of the anterior bodies, into a number of 

 distinct alveoli. These alveoli are far more distinct in some 

 parts of the bodies than in others. The nerve-trunks uniting 

 the bodies with the spinal nerves ^re (at least in specimens 

 hardened in picric and chromic acids) very difficult to see, and 

 I have failed to detect that they are connected with special 

 parts of the bodies, or that the separate alveoli differ much as 

 to the nature of their constituent cells. The aortic branches to 

 the bodies are larger than in the previous stage, and the bodies 

 themselves fairly vascular. 



By stage Q (PL xviii. fig. 9) two distinct varieties of cells 

 are present in these bodies. One of these is large, angular, and 

 strikingly resembles the ganglion cells of the spinal nerves at 

 the same period. This variety is found in separate lobules or 

 alveoli on the inner border of the bodies. I take them to be 

 true ganglion cells, though I have not seen them in my sections 

 especially connected with the nerves. The cells of the second 

 variety are also aggregated in special lobules, and are very 

 markedly smaller than the ganglionic cells. They form, I 

 imagine, the cells of the true suprarenal tissue. A.t this and 

 the earlier stage lymphoid tissue, like that surrounding the 

 suprarenal bodies in the adult, is found adjacent to these 

 bodies. 



Stage Q forms my last embryonic stage, and it may perhaps 

 be asked on what grounds I regard these bodies as suprarenal 

 bodies at all and not as simple sympathetic ganglia. 



My determination mainly rests on three grounds : (1) That 

 a branch from the aorta penetrates these bodies and maintains 

 exactly the same relations to them that the same branches of 

 the aorta do in the adult to the true suprarenal bodies. (2) That 

 the bodies are highly vascular. (3) That in my last stage they 

 become divided into a ganglionic and a non-ganglionic part, 

 with the same relations as the ganglia and suprarenal tissue in 

 the adult. These grounds appear to me to afford ample justifica- 

 tion for my determinations, and the evidence adduced above 



