DEVELOPMENT OF ELASMOBRANCH FISHES. 279 



In a somewhat older embryo there was connected with the 

 anterior vas efFerens a peculiar structure represented on PL xix. 

 fig. 7, r. St ? which strangely resembled the opening of an 

 ordinary segmental tube, but as I could not find it in the 

 younger embryo, this suggestion as to its nature, is, at the 

 best, extremely hazardous. If, however, this body really is the 

 remnant of a segmental opening, it would be reasonable to 

 conclude that the vasa efferentia are buds from the segmental 

 tubes as opposed to their openings ; a mode of origin which 

 is not incompatible with the discoveries of Dr SpengeL I 

 have noticed a remnant, somewhat similar to that in the 

 Scyllium embryo, close to the hindermost vas efferens in an 

 embryo Squatina (PI. XIX. fig. 8, r.st ?). 



With reference to the development of the longitudinal 

 canal of the Wolffian body, I am without observations, but it 

 appears to me to be probably a further development of the 

 outgrowths of the vesicles of each segmental tube, which were 

 described in connection with the development of the segmental 

 tubes, p. 262. Were an anterior outgrowth of one vesicle to 

 meet and coalesce with the posterior outgrowth of the preceding 

 vesicle, a longitudinal canal such as actually exists would be 

 the result. The central canal of the base of the testes and 

 the network connected with it in the adult (PI. XIX. fig. 4), 

 appear to be derivatives of the vasa efferentia. 



I am thus compelled to leave open the question of the real 

 nature of the vasa efferentia, but am inclined to regard them 

 as outgrowths from the anterior segmental tubes, though not 

 from their open terminations. 



My views upon the homologies of the various parts of the 

 urinogenital system, the development of which has been de- 

 scribed in the present chapter, have already been expressed in 

 a paper on Urinogenital organs of Vertebrates ^ Although 

 Kolliker's^ discovery of the segmental tubes in Aves, and the 

 researches of Spengel^ Gasser'', Ewart^ and others, have ren- 



^ Journal of Anatomy and Physiology, Vol. x. 



' Entivicklungsgeschichte des Menschen u. der hoheren Tliiere. 



3 Loc. cit. 



4 Beitrage zur Entwicklungsg. d. Allantois d. Muller'schen Gauge u. d. Afters. 



5 Abdominal Pores and Urogenital Sinus of Lamprey, Journal of Anatoviy 

 and Physiology, Vol, x. p. -iSS. 



