254 SEGMENTAL TUBES. 



bladders are absent in tbe female, though possibly represented 

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

 oviducts, 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, Segmentaltricliter, 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 seg- 

 mental openings, and the tubes connected with them as seg- 

 mental 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 ^ 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 certainty, but in one young example, which had left the 

 egg but a short time, there appeared to be at least fourteen 

 present. According 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 anterior 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 PL xix. fig. 5, is represented 



1 The term eegment will bo more accurately defined below. 



