ON THE DEVELOPMENT OF THE ELASMOBRANCH FISHES. 361 



ciliated opening into the pleuro-peritoneal cavity. It will, 

 perhaps, be found, when the development of the Marsipo- 

 branchii is more carefully studied, that there are primitively 

 a number of such openings.^ The Oviduct, when present, 

 arises in other vertebrates 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 de 

 velopment 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 or two words 

 about the development of the Ovary. In both sexes the 

 germinal 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. 13, p, ov). 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, how- 

 ever, the thickened epithelium on the knob grows more and 

 more conspicuous, and develops 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 epithe- 

 lium on the ridge, though containing 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 become the Ovaries. 



' While correcting the proofs of this paper I have come across a memoir 

 of W. Miiller (' Uber die Persistenz der Urniei'e bei Myxiue Glutiuosa,' 

 'Jenaische Zeitschrift/ vol. vii, 1873), in which he mentions tliat in Myxine 

 the upper end of the Walffian duct communicates by numerous openings 

 with the pleuro-peritoneal cavity; this gives to the suggestion in the 

 text a foundation of fact. 



