278 VASA EFFERENTIA. 



extremely important discovery, that in young Amphibians each 

 Malpighian body in the region of the generative ducts, in 

 addition to receiving the vasa efferentia, is connected with a 

 fully developed segmental 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 con- 

 dition 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 Elasmo- 

 branchs, 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 seg- 

 mental 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. XIX. 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 pro- 

 bably connected by a longitudinal canal in the Wolffian body, 

 but this could not be clearly seen. In the segment immedi- 

 ately behind the last vas efferens was a fully developed seg- 

 mental 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 ex- 

 amination of still younger embryos. 



