126 W. F. B. WELDON. 



nephros in the male^ where it forms the complicated network 

 of the epididymis, while in the female it by no means retains 

 its primitive characters. 



In Amphibians and Reptiles the intimate connection of the 

 two sets of organs, and the great similarity between their 

 means of blood supply — each receiving a portion of venous 

 blood from the trunk or hind limbs, which passes through the 

 organ (kidney or suprarenal as the case may be), to go to the 

 vena cava — are surely most easily explained by supposing both 

 organs to be parts of a single primitive structure, which are 

 undergoing specialisation in different directions. 



The very general absence of suprarenals, as separate struc- 

 tures, in Teleosteans, together with the existence of a peculiarly 

 modified head kidney, has already been mentioned as leading 

 to the same conclusion. The connection between the supra- 

 renals and more or fewer of the sympathetic ganglia which 

 exists in so many forms (Elasmobranchs, Reptiles, Birds, 

 Mammals) can hardly be other than secondary. 



The development of the bodies in question has been 

 worked out in Elasmobranchs by Balfour,^ in Reptiles by 

 Braun,^ and in Mammals by Mitsukuri^ and Janosik.* In all 

 these forms the first recognisable rudiment of a suprarenal is 

 in the form of a compact mass of mesoblastic tissue, lying 

 dorsal to the Wolffian body, between it and the aorta; and there- 

 fore just at the base of the ridge of the commencing generative 

 epithelium. The cells composing this mass envelope a certain 

 number of sympathetic ganglia ; forming the cortical part of 

 the adult suprarenal, while the cells of the ganglia form its 

 central part. The question of the homologies of the cortical 

 part of the suprarenals must, if it is to be settled by embryo- 

 logical evidence at all, be decided by observations on the mode 

 of origin of the primitive cell-mass from which the cortical sub- 

 stance of the adult organ arises. On this point there is, however, 



' ' Elasmobrancli Fishes.' 



- Loc. cit. 



3 ' Quart. Journ. Micr. Sci.,' Jan., 1882. 



" ' Archiv fur Mikroscopische Anatomic,' xxii Band, 1883. 



