ON THE SUPRARENAL BODIES OK VERTEBRATA. 185 



chief difference between his figure and mine being that he hasj 

 having overlooked the earlier stages, been led to an erroneous 

 form of opinion as to the mode of origin of the tissue which 

 he figures. From this point onwards, however, his observa- 

 tions as to the histological differentiation of the cortical 

 substance, and the entrance into it of the medullary ganglion 

 cells are so complete that it is needless to attempt to add 

 anything to his description. 



In Pristiurus, as in other forms, the early history of the 

 suprarenals has only been traced from a point at which a meso- 

 blastic rudiment, distinct from all other organs, already existed. 

 This is the stage at which Balfour, in the passage already 

 quoted, begins his account of their development. I propose, 

 therefore, to trace the history of this blastema in Pristiurus, 

 which is the only Elasmobranch in which I have observed it. 



In figs. 9 and 10 are shown two consecutive sections through 

 a Pristiurus embryo 8 mm. in length, at a stage corresponding 

 to Balfour's Stage I — the stage immediately preceding that 

 in which he begins the history. Both these sections pass 

 through the opening into the body cavity of the same seg- 

 mental tube, which is seen to give off, just after the narrowing 

 of its funnel shaped opening into the body cavity, a small 

 process (s. r.) ,which projects towards the root of the mesentery. 

 In fig. 9, which passes through the middle of this process, it 

 is seen to have a very considerable lumen. In fig. 10 it is 

 cut tangentially, and the lumen is therefore not apparent. 



In figs. 11 and 12, from a slightly older embryo, this diver- 

 ticulum of the segmental tubule is seen to have obtained a 

 considerable size, and to project quite to the middle line over 

 the root of the mesentery. It is not seen in the figure to be 

 joined by a similar structure from the opposite side, because 

 the section copied was so oblique that the right hand side was 

 intervertebral. In the next following section, however (fig. 13), 

 the wall of the outgrowth of the other side is cut. 



In an embryo of between 9 and 10 mm. the outgrowth has 

 become solid, and lies just over the root of the mesentery, as 

 shown in fig. 14 ; further, at this stage the outgrowths have 



