DEVELOPMENT OF THE ELASMOBRANCH FISHES. IOI 



They have further acquired a communication with the 

 Oviduct, in the form of a narrow duct passing from each of them 

 into an Oviduct a short way before the latter opens into the 

 cloacal dilatation of the alimentary canal. 



The canals formed by the primitive involution leading from 

 the pleuro-peritoneal cavity into the Wolffian duct have become 

 much more elongated, and at the same time narrower. One of 

 these is shewn in fig. 1 3, p w d. 



Any doubt which could possibly be entertained as to the 

 true character of the ducts whose development I have described 

 is entirely removed by the development of the tubules of the 

 Wolffian body. In the still later stage than this further proofs 

 are furnished involving the function of the Oviduct. At the 

 period when the olfactory lobes have become so developed as to 

 render the head of the typical elongated shape of the adult, I find 

 that the males and females can be distinguished by the presence 

 in the former of the clasping appendages 1 . I find at this stage 

 that in the female the front ends of the Oviducts have approached 

 the middle line, dilated considerably, and commenced to exhibit 

 at their front ends the peculiarities of the adult. In the male 

 they are much less conspicuous, though still present. 



At the same time the tubules of the Wolffian body become 

 much more numerous, the Malpighian tufts appear, and the ducts 

 cease almost, if not entirely, to communicate with the pleuro- 

 peritoneal cavity. I have not made out anything very definitely 

 as to the development of the Malpighian tufts, but I am inclined 

 to believe that they arise independently in the mesoblast of the 

 intermediate cell mass. 



The facts which I have made out in reference to the develop- 

 ment of the Wolffian duct, especially of its arising as a series 

 of involutions from the pleuro-peritoneal cavity, will be found, 

 I believe, of the greatest importance in understanding the true 

 constitution of the Wolffian body. To this I will return directly, 

 but first wish to clear the ground by insisting upon one preli- 

 minary point. 



From their development the Oviduct and Wolffian body 

 appear to stand to each other in the relation of the Wolffian 



1 For the specimens of this age I am indebted to Professor Huxley. 



