The Comparative Histology of the Suprarenal Capsules. 299 



find large cells resembling nerve-cells, except that the protoplasm is 

 full of the brown pigment produced by the action of the bichromate 

 of potassium^). Then there are some smaller cells, less like nerve- 

 cells and more like the proper medullary cells. These ivould appear 

 to he transition forms hetween the tivo. The proper cells of the 

 medullary substance are so like those of the Anura and Reptilia that 

 they do not deserve a separate description. 



2. Anura. 



There is practically no difference between the various species of 

 frogs and toads as regards the minute structure of the suprarenal 

 capsules. In these animals the suprarenals are golden-yellow streaks 

 on the ventral surface of the kidney, of about 15 mm. in length in 

 the common frog to about 28 mm. in a good sized toad. Their width 

 varies in a similar manner from 1 to about 3 mm. But their dimensions 

 vary very considerably according to the size and development of the 

 particular individual. In a good sized specimen the suprarenals present 

 on the ventral surface of the kidneys a very beautiful appearance, 

 forming on each side a series of irregular arcs with their convexity 

 outwards, and varying in width from place to place. Their colour is 

 of a bright yellow, of a somewhat fatty aspect, and their surface is 

 marbled with veins running in all directions. Their average dimensions 

 are given above, but it is noteworthy that in both frogs and toads, 

 although the suprarenal reaches nearly up to the anterior end of the 

 kidney, it always ceases at a point anterior to the posterior fifth of 

 that organ. 



The adrenal is not quite continuous, but is broken up on each 

 side into a varying number of portions, separated by slight intervals. 

 With a lens, or sometimes even with the naked eye, they are seen to 

 consist of a series of parallel lines presenting a distinctly lobulated 

 appearance. 



The blood-supply appears to be the same as that of the kidney 

 substance, i. e. it receives arterial blood from the dorsal aorta and 



^) These medullary cells and those of Reptilia possess a slight yellowish-brown 

 coloration even in a fresh state. 



