1884.] Origin of the Suprarenal Bodies of Vertebrates. 423 



connexion with the segmental duct, and the one or two glomeruli 

 (both shown by Wilhelm Miiller to exist in the embryo of Myxine) 

 had disappeared, all that remained being a plexus of tubules, opening 

 into the pericardium, but without any other opening whatever, and 

 entirely unconnected with the rest of the kidney. This plexus was 

 closely surrounded by a network of blood-vessels, and the larger 

 tubules contained altered blood-corpuscles. 



In seeking for a parallel, among other Vertebrates, to this peculiar 

 modification of a portion of the kidney, I was struck by the following 

 facts : 



In Teleostei and Ganoids, Balfour has shown* that the head kidney 

 is often replaced, in the adult, by a mass of lymphatic tissue, richly 

 supplied with vessels. Emery has studied the development of this 

 tissue ; he finds in the embryo of many Teleostei, at an early stage, a 

 single pronephric funnel, communicating with the segmental duct ; 

 the rest of the " intermediate cell-mass," being an undifferentiated 

 blastema surrounding the duct. In later development, only a portion 

 of this tissue becomes converted into renal tubules ; the rest remaining 

 through life as " lymphatic " tissue, richly supplied with vessels. f 



Now the Teleostei and the Cyclostomes are the only Vertebrates 

 ievoid of suprarenals ; and where these latter organs exist, they are 

 always closely connected with the kidney, having, in reptiles and 

 amphibians, a "vena portas," corresponding to the "renal portal 

 system " of the kidney, and being in male reptiles situated in the 

 mesorchium, side by side with the longitudinal network of the testis. 



It therefore seemed worth while to re-examine the development of 

 the " cortical " part of the suprarenal bodies. This I have done in 

 Pristiurus, in Lacerta, and in the chick, finding it to be derived in each 

 case from a portion of the mesonephric tubules. 



In Lacerta muralis, the segmental vesicles, when they have become 

 connected by the usual c\3 -shaped cords with the Wolffian duct, become 

 invaginated, and form glomeruli. In the region of the future genera- 

 tive ridge, as each glomerulus begins to invaginate, before a blood- 

 vessel enters it, its mesenteric border (that opposite to the connexion 

 with the oo -shaped segmental tube) thickens, and becomes more than 

 one cell thick, the rest of its wall being never, at any period of its 

 existence, formed of more than a single layer of cells. As the genera- 

 tive ridge develops, the thickened portion of each glomerulus increases, 

 and gives rise to a process divided into two branches, one dipping 

 ventral wards into the generative ridge, the other going dorsally 

 between the kidney and the cardinal vein. Both branches are at first 

 histologically indistinguishable, being alike composed of rounded 

 cells, pressed closely one against another. 



* " Quart. Journ. Mic. Sci.," 1882, and " Phil. Trans.," 1882. 

 t " Atti dell' Academia dei Lincei," 1882. 



