NOTES ON ELASMOBRANOH DEVELOPMENT. 567 
zeiger,’ vol. ili, p. 445, in which he calls attention to the fact 
that Kowalevsky, in a paper published in Russian in about 
1870, was the first to describe it correctly. That Kowalevsky’s 
description, if correct, as maintained by Kastschenko, should 
have been overlooked, is of course attributable to the fact of 
its being written in Russian, and not reproduced in any of the 
more commonly known European languages. It seems a great 
pity that an observer of the eminence of Kowalevsky should 
thus secrete his work and render it unavailable to science. 
Kastschenko’s account of the matter is as follows: 
“The closure of the medullary tube presents in the dog- 
fishes interesting peculiarities, which were first discovered and 
correctly described by A. Kowalevsky..... The medullary 
folds are continuous at their hinder ends with the caudal 
lobes, and by means of the latter with the general edge of the 
blastoderm. Each caudal lobe presents a marked knee-shaped 
bend, the point of which is directed backwards.. The lateral 
limbs of the paired caudal lobes approach one another on the 
ventral side of the embryo; and when the medullary folds 
fuse on the dorsal surface the adjacent caudal lobes also fuse. 
By the fusion of the former the medullary tube is formed, and 
by the fusion of the latter the neurenteric canal and the hind 
gut. The hind gut, therefore, is the immediate continuation 
of the medullary tube, and the neurenteric canal must be 
regarded as nothing else than a portion of the blastopore. 
Further forwards the hind gut remains for some time open 
ventralwards, but eventually this opening also fuses, the anus 
appearing considerably later in the same place.” 
This account, however, as will be gathered from my descrip- 
tion, does not give the whole gist of the matter. It fails to 
notice the slit-like form of the dorsal part of the blastopore 
which perforates the floor of the medullary canal, and the 
author does not appear to understand, or at any rate fails to 
draw attention to the fact that the ventral opening leading 
into the hind gut is part of the blastopore, and is continuous 
with the slit-like non-embryonic part of the blastopore running 
along the yolk. ‘The only point in which it supplements 
