484 DEVELOPMENT OF ELASMOBRANCH FISHES. 



bladders are absent in the female, though possibly represented 

 by the bladder-like dilatations of the Wolffian duct. The ovi- 

 ducts, whose anatomy is too well known to need description, 

 open independently into the general cloaca. 



Since the publication of Professor Semper's researches on 

 the urinogenital system of Elasmobranch fishes, it has been well 

 known that, in most adult Elasmobranchs, there are present a 

 series of funnel-shaped openings, leading from the perivisceral 

 cavity, by the intermediation of a short canal, into the glandular 

 tubuli of the kidney. These openings are called by Professor 

 Semper, Segmentaltrichter, and by Dr Spengel, in his valuable 

 work on the urogenital system of Amphibia, Nephrostomen. In 

 the present work the openings will be spoken of as segmental 

 openings, and the tubes connected with them as segmental 

 tubes. Of these openings there are a considerable number in 

 the adults of both sexes of Scy. canicula, situated along the 

 inner border of each kidney. The majority of them belong to 

 the Wolffian body, though absent in the extreme anterior part 

 of this. In very young examples a few certainly belong to 

 the region of the kidney proper. Where present, there is one 

 for each segment 1 . It is not easy to make certain of their 

 exact number. In one male I counted thirteen. In the female 

 it is more difficult than in the male to make this out with cer- 

 tainty, but in one young example, which had left the egg but a 

 short time, there appeared to be at least fourteen present. Ac- 

 cording to Semper there are thirteen funnels in both sexes a 

 number which fairly well agrees with my own results. In the 

 male, rudiments of segmental tubes are present in all the an- 

 terior segments of the Wolffian body behind the vasa efferentia, 

 but it is not till about the tenth segment that the first complete 

 one is present. In the female a somewhat smaller number of 

 the anterior segments, six or seven, are without segmental tubes, 

 or only possess them in a rudimentary condition. 



A typical segment of the Wolffian body or kidney, in the 

 sense in which this term has been used above, consists of a 

 number of factors, each of which will be considered in detail 

 with reference to its variations. On PI. 20, fig. 5, is represented 



1 The term segment will be more accurately defined below. 



