DEVELOPMENT OF ELASMOBRANCH FISHES. 283 



the (1) Wolfficaii duct dorsally, which remains continuous with 

 the excretory tubules of the kidney, and ventrally (2) the 

 oviduct or Mullerian duct in the female, and the rudiments 

 of this duct in the male. In the female the formation of 

 these ducts takes place by a nearly solid rod of cells, being 

 gradually split off from the ventral side of all but the foremost 

 part of the original segmental duct, with the short undivided 

 anterior part of which duct it is continuous in front. Into 

 it a very small portion of the lumen of the original seg- 

 mental duct is perhaps continued (PL XX. fig. 1 A, etc.). The 

 remainder of the segmental duct (after the loss of its anterior 

 section and the part split off from its ventral side) forms the 

 Wolffian duct. The process of formation of the ducts'^ in the 

 male chiefly differs from that in the female in the fact of the 

 anterior undivided part of the segmental duct, which forms 

 the front end of the Miillerian duct, being shorter, and in the 

 column of cells with which it is continuous being from the 

 first incomplete. 



The tubuli of the primitive excretory organ undergo further 

 important changes. The vesicle at the termination of each 

 segmental tube grows forwards towards the preceding tubulus, 

 and joins the fourth section of it close to the opening into the 

 Wolffian duct (PL XX. fig. 10). The remainder of the vesicle 

 becomes converted into a Malpighian body. By the first of 

 these changes a connection is established between the suc- 

 cessive segments of the kidney, and though this connection is 

 certainly lost (or only represented by fibrous bands) in the 

 anterior part of the excretory organs in the adult, and very 

 probably in the hinder part, yet it seems most probable that 

 traces of it are to be found in presence of the secondary Mal- 

 pighian bodies of the majority of segments, which are most 

 likely developed from, it. 



Up to this time there has been no distinction between the 

 anterior and posterior tubuli of the primitive excretory organ 

 which alike open into the Wolffian duct. The terminal 

 division of the tubuli of a considerable number of the hinder- 

 most of these (ten or eleven in Scyllium canicula), either in 

 some species elongate, overlap, and eventually open by aper- 

 tures (not usually so numerous as the separate tubes), on nearly 



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