104 DEVELOPMENT OF THE ELASMOBRANCH FISHES. 



as a single involution, strongly supporting the view that its 

 mode of formation, in the Dog-fish is fundamentally merely an 

 involution. 



The duct of the testes is, I have little doubt, derived from 

 the anterior part of the Wolffian body ; if so, it must be looked 

 upon as not precisely equivalent to the Oviduct, but rather 

 to a series of coalesced organs, each equivalent to the Oviduct. 

 The Oviduct is in the Elasmobranchii, as in other vertebrates, 

 primitively developed in both sexes. In the male, however, 

 it atrophies. I found it still visible in the male Torpedos, 

 though much smaller than in the females near the close of intra- 

 uterine life. 



Whether or not these theoretical considerations as to the 

 nature of the Wolffian body and Oviduct are correct, I believe 

 that the facts I have brought to light in reference to the develop- 

 ment of these parts in the Dog-fish will be found of service 

 to every one who is anxious to discover the true relations of 

 these parts. 



Before leaving the subject I will say one on two words 

 about the development of the Ovary. In both sexes the ger- 

 minal epithelium (fig. 13) becomes thickened below the Oviduct, 

 and in both sexes a knob (in section but really a ridge) comes 

 to project into the pleuro-peritoneal cavity on each side of 

 the mesentery (fig. i^,pov}. In both sexes, but especially 

 the females, the epithelium on the upper surface of this ridge 

 becomes very much thickened, whilst subsequently it elsewhere 

 atrophies. In the females, however, the thickened epithe- 

 lium on the knob grows more and more conspicuous, and de- 

 velops a number of especially large cells with large nuclei, 

 precisely similar to Waldeyer's (loc. cit.} "primitive ova" of the 

 Bird. In the male the epithelium on the ridge, though con- 

 taining primitive ova, is not as conspicuous as in the female. 

 Though I have not worked out the matter further than this at 

 present, I still have no doubt that these projecting ridges be- 

 come the Ovaries. . 



Wolffian duct communicates by numerous openings with the pleuro-peritoneal cavity ; 

 this gives to the suggestion in the text a foundation of fact. 



