242 ADAM SEDGWICK. 



zeiger/ vol. iii, 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 



