514 DEVELOPMENT OF ELASMOBRANCH FISHES. 



parts of the Wolffian ducts, in the male ; or in other species 

 become modified in such a manner as to pour their secretion into 

 a single duct on each side, which opens in a position correspond- 

 ing with the numerous ducts of the other type (woodcut, fig. 8). 

 It seems that both in Amphibians and Elasmobranchs the type 

 with a single duct, or approximations to it, are more often found 

 in the females than in the males. The subject requires however 

 to be more worked out in Elasmobranchs 1 . In both groups the 

 modified posterior kidney-segments are probably equivalent to 

 the permanent kidney of the amniotic Vertebrates, and for this 

 reason the numerous ducts of the first group or single duct of 

 the second were spoken of as ureters. The anterior tubuli of 

 the primitive excretory organ retain their early relation to the 

 Wolffian duct, and form the Wolffian body. 



The originally separate terminal extremities of the Wolffian 

 ducts always coalesce, and form a urinal cloaca, opening by 

 a single aperture situated at the extremity of a median papilla 

 behind the anus. Some of the abdominal openings of the 

 segmental tubes in Scyllium, or in other cases all the openings, 

 become obliterated. 



In the male the anterior segmental tubes undergo remark- 

 able modifications. There appear to grow from the first three 

 or four or more of them (though the point is still somewhat 

 obscure) branches, which pass to the base of the testis and there 

 unite into a longitudinal canal, form a network, and receive 

 the secretion of the testicular ampullae (woodcut 9, nf). These 

 ducts, the vasa efferentia, carry the semen to the Wolffian body, 

 but before opening into the tubuli of this they unite into the 

 longitudinal canal of the Wolffian body (l.c], from which pass off 

 ducts equal in number to the vasa efferentia, each of which 

 normally ends in a Malpighian body. From the Malpighian 

 body so connected start the convoluted tubuli of what may be 

 called the generative segments of the Wolffian body along 

 which the semen is conveyed to the Wolffian duct (v. d). The 

 Wolffian duct itself becomes much contorted and acts as vas 

 deferens. 



1 The reverse of the above rule is the case with Raja, in the male of which a closer 

 approximation to the single-duct type is found than in the female. 



