iv THE SUPEAEENAL ORGANS 283 



chemical or physical reaction, in that it takes on a deep yellow or 

 brown colour when treated with salts of chromic acid. Hence it is 

 convenient, and usual, to apply to it a name expressive of this reaction- 

 such as Chromophile (Stilling), Chromaffine (Kohn) or Phaeochrome 

 (Poll). 



The cortical tissue has also characteristic features — in particular 

 the fact that its cytoplasm contains numerous granules of lipoid or 

 fat-like substance, soluble in Ether, Xylol, etc., staining deeply with 

 various Aniline stains, and giving the characteristic black with Osmic 

 Acid. For masses of this tissue the name Interrenal organ may be 

 used (Balfour) which although a topographical term like cortical 

 substance has the advantage of being correct for vertebrates in 

 general during at least the early stages of their development. 



Of the more primitive groups of gnathostomatous Vertebrates 

 only the Elasmobranchs and the Amphibians have been studied 

 carefully in regard to the development of these organs and we shall 

 consequently use them as illustrating the general mode of develop- 

 ment which, with variations in detail, holds throughout the groups 

 dealt with in this volume. 



Elasmobeanchii. 1 — The Interrenal organs are here interrenal in 

 position through life, forming either one (Sharks) or a pair (Skates 

 and Eays) of elongated bodies lying in the region of the mesial plane 

 and extending for some distance opposite the hinder part of the 

 opisthonephros. 



In Scyllium (Poll) the interrenal makes its first appearance 

 (7 mm. embryo) in the form of a number of irregularly distributed 

 thickenings of the splanchnic mesoderm in the region of the root 

 of the mesentery, just ventral to the dorsal aorta. The possibility 

 of metameric arrangement in the very earliest stages does not seem 

 to be absolutely excluded but there is no evidence of this so far. 

 The rudiments are most numerous in the genital region but they 

 occur as far forwards as the hind end of the pronephros and back as 

 far as the cloaca. The rudiments of the two sides, projecting towards 

 the median plane, meet and become continuous, and as antero- 

 posterior fusion also comes about, the rudiment takes the form 

 (10 mm. embryo) of a cellular rod lying beneath the dorsal aorta 

 and above the mesenteric root, and for a time still continuous with 

 the splanchnic mesoderm which gave it origin. Por a time there is 

 close apposition, amounting to apparent continuity of tissue, between 

 this rod. and the opisthonephric nephrotomes lying on either side of 

 it, but it is doubtful whether any special morphological significance 

 is to be attached to this. In embryos of 16-28 mm. in length the 

 interrenal organ gradually becomes separated in a tailward direction 

 both from the coelomic epithelium and the nephrotomes, and assumes 

 its definitive form. 



Only the tailward part of the series of original rudiments 



1 The best general account of the development of the Suprarenal organs is that by 

 Poll (1905). 



