Tlie Comparative Histology of the Stiprarenal Capsules. 285 



nervous system. But medullary substance when injected into the venous 

 system of a living mammal even in the smallest quantity, always 

 causes a marked rise of blood-pressure. I feel justified, therefore, in 

 dismissing these groups of cells from consideration as the analogues 

 of the suprarenal medulla, at any rate as the physiological analogues. 

 Whether or no there are any suprarenal bodies in Invertebrata must 

 remain an open question for the present. 



III. Acrania. Amphioxus. 

 Nothing is known of the suprarenal bodies in Amphioxus. There is 

 no mention of them in the text-books or in the monographs upon this 

 animal. I have myself examined several individuals without finding 

 anything which suggested the existence of either the cortical or 

 medullary representatives of these organs. It would however be rash 

 in the present state of our knowledge to assume that Amphioxus has 

 nothing corresponding to the suprarenal bodies. 



IV. Cyclostomata. 



As early as 1827 Rathke \93] described certain "white-specks" 

 on the cardinal veins of Ammocoetes which he thought were supra- 

 renals. In the following year a note appears in the text of "Burdach's 

 Physiologie" (Bd. XIX. No. 2. p. 601) signed by Rathke in which he 

 suggests that the pronephros or head-kidney and suprarenal bodies 

 may be homologous. In 1843 appeared the well known description of 

 J. Miiller's "Clustered gland" in Myxinoids. Later this Author changed 

 his opinion and thought it was the thymus. 



Ecker [32, 33] in 1846 described a new structure in Petromyzon 

 as a suprarenal body, an organ triangular in section on the inner wall 

 of the posterior cardinal sinus. Stannius [107 — 110] and Leydig [70] 

 considered the bodies pointed out by Rathke and J. Müller to be the 

 suprarenal bodies. 



In 1884, Weldon [124] described the head-kidney of Bdellostoma 

 and believed that in this animal the pronephros has become modified 

 so as to form an organ functionally analogous to the suprarenals. 

 Later this writer expands this view [-^-^] and in Wiedersheim's text- 

 book [126, 127] we find Rathke's original suggestion revived: — 



