BLOOD GLANDS 347 



the median line between the two kidneys, or is unsymmetrically 

 placed on the ventral surface of either kidney.-' Sometimes (e.g. 

 in Baia) the inter-renals are paired, in which case they are applied 

 to the inner and hinder margins of the kidneys. In the Sturgeon 

 (Acipenser sturio) the " supra-renals " appear as numerous " ochre- 

 yellow " bodies, variable in size and distribution (Fig. 203, B). 

 Some of them are visible on the surface of the kidneys, while 

 others are scattered about in their substance, but on the whole 

 are more anteriorly placed than in Teleosts. In the latter group 

 the "supra-renals" are usually two in number (Fig. 203, C), but 

 may be as many as five or reduced to one. They are disposed 

 either on the ventral or the dorsal surface of the kidneys, 

 generally near their hinder extremities, or more or less deeply 

 embedded in their substance. Besides these bodies there are 

 also chromaffin cells in the walls of the anterior cardinal veins.^ 

 Histologically, the paired segmentally arranged bodies of 

 Elasmobranchs differ considerably in structure from the inter- 

 renal bodies, the former resembling the " medulla," while the 

 inter-renals, as well as the so-called supra-renals of Aciioenser, 

 exhibit a striking resemblance to the alveolar " cortical " sub- 

 stance of the Mammalian supra-renals.^ In Cyclostomes the 

 cortex is apparently represented by the lobules of cells along the 

 posterior cardinal veins and the medulla by the " chromaffin " 

 cells, while in Teleosts the cortex and the medulla have their 

 respective counterparts in the supra-renals and the " chromaffin " 

 cells in the walls of the anterior cardinal veins. It may be 

 concluded, therefore, that Elasmobranchs, Cyclostomes, and 

 Teleosts possess anatomically distinct representatives of both the 

 " meduUa " and " cortex " of Mammalia, although the Sturgeon 

 is at present only known to possess the equivalent of the 

 " cortex." In Amphibia, Eeptilia, and Aves both " cortex " and 

 " medulla " are present, and in the varying intimacy of their 

 relations offer a transition to the Mammalian arrangement of a 

 central medulla closely invested by a sheath of cortical substance. 

 A more or less intimate connexion exists between the paired 

 supra-renals of Elasmobranchs and the sympathetic nervous 



' Vincent, Trans. Zool. Hoc. xi'v. Part iii, 1897, p. 41. For bibliography see 

 Vincent, Internal. Monatsschr. f. Anat. u. Phys. xv. 1898, p. 819. 



^ Giacomini, quoted by Swale Vincent, Journ. Anat. and Phys. xxxviii. 1903, 

 p. 41. 



' Vincent, op. cit. pp. 32, 33. 



