508 DEVELOPMENT OF ELASMOBRANCH FISHES. 



tube opening into the body-cavity. In Amphibians, therefore, 

 it is improbable that the vasa efferentia are products of the open 

 extremities of the segmental tubes, considering that these latter 

 are found in their unaltered condition at the same time as the 

 vasa efferentia. When it is borne in mind how strikingly similar 

 in most respects is the arrangement of the testicular ducts in 

 Amphibia and Elasmobranchs, it will not easily be credited that 

 they develope in entirely different methods. Since then we find 

 in Amphibians fully developed segmental tubes in the same 

 segments as the vasa efferentia, it is difficult to believe that 

 in Elasmobranchs the same vasa efferentia have been developed 

 out of the segmental tubes by the obliteration of their openings. 



I set myself to the solution of the origin of the vasa effe- 

 rentia by means of surface views, after the parts had been made 

 transparent in creosote, but I have met with great difficulties, and 

 so far my researches have only been partially successful. From 

 what I have been able to see of Squatina and Acanthias, I am 

 inclined to think that the embryos of either of these genera 

 would form far more suitable objects for this research than 

 Scyllium. I have had a few embryos of Squatina which were 

 unfortunately too old for my purpose. 



Very early the vasa efferentia are fully formed, and their 

 arrangement in an embryo eight centimetres long is shewn 

 in PI. 20, fig. 6, v.e. It is there seen that there are six if not 

 seven vasa efferentia connected with a longitudinal canal along 

 the base of the testes (Semper's central canal of the testis), and 

 passing down like the segmental tubes to spaces between the 

 successive segments of the Wolffian body. They were probably 

 connected by a longitudinal canal in the Wolffian body, but this 

 could not be clearly seen. In the segment immediately behind 

 the last vas efferens was a fully developed segmental tube. This 

 embryo clearly throws no light on the question at issue except 

 that on the whole it supports Semper's views. I further failed to 

 make out anything from an examination of still younger embryos. 



In a somewhat older embryo there was connected with the 

 anterior vas efferens a peculiar structure represented on PI. 20, 

 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, 



