The Comparative Histology of the Suprarenal Capsules. 287 



une série d'acinés tapissés par un epithelium columnaire et pourvus 

 d'une lumière; en outre il existe quelques cellules pigmentaires éparses 

 cà et là." 



Pettit is unable to decide whether this structure is homologous 

 with the suprarenal bodies of Teleosts or not. 



V. Pisces. 

 1. Masmobranchii. 



In Elasmobranch fishes two distinct sets of structures are found, 

 both of which have from time to time been described as suprarenal 

 bodies. These two structures correspond the one to the medulla and 

 the other to the cortex of the suprarenal capsule in the higher 

 Vertebrata^). 



Paired Suprarenal Bodies. The following account differs in some 

 points from that which I gave in April of last year [116]. Since that 

 time I have determined that these bodies correspond physiologically 

 to the medulla of the suprarenals of the higher Vertebrata [120^ 121] 

 and that they contain the same chromogen [81]. We shall see that 

 the histological structure also is analogous. 



The gross anatomy of these bodies need not detain us. They 

 are situated on branches of the aorta, segmen tally arranged, and 

 extend on each side of the vertebral column from the front part of 

 the sinus of Monro to the posterior end of the kidney. The anterior 

 pair are elongated and correspond usually to three or four segments'). 



The structure of these bodies is very complex and difficult to 

 describe even when the preparations are successfully made. It will 

 be desirable, however, to enter into as much detail as possible, since 

 these organs represent the primitive type of suprarenal medulla in 

 Vertebrates. 



It will be convenient first of all to describe the structure of 

 the first pair, the so-called "axillary hearts" and then to proceed to 

 the description of the bodies which lie posterior to them. 



^) This view was first put forward by Balfour [6] p. 664. 

 ^) For drawings of these bodies see 114 of bibliography. 



