ON THE SUPRARENAL BODIES OF YERTEBRATA. 143 
chief difference between his figure and mine being that he has, 
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 mesenterv. 
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 mesenterv, as 
shown in fig. 14 ; further, at this stage the outgrowths have 
