NEMERTEA ENOPLA 661 



lateral gonopores, that in this way became ventral (Drepano- 

 phoridae-Siboga expedition) ; the V-shaped gonadial sac still 

 is quite clear. In D. albolineatus (Text-fig. 24) the 

 gonad acquired another, third part, that lies in this ' Seiten- 

 rippe ', and the ventral primary leg was somewhat reduced ; 

 but all three parts are present. In the Pelagica the develop- 

 ment of the ventral ovaries cannot have taken place in this 

 way, as all traces of the V-shaped sac or of many ovaries are 

 absent, and real dorsal gonopores are unknown in both sexes. 

 The only cases, as far as our present knowledge goes, in which 

 the gonopores are not ventral but lateral seem to be the testes 

 of Armaueria and Parabalaenanemertes, and even in these the 

 testes open partly ventrolaterally. As to the ovaries they are 

 rather uniformly built, and there is a reduction of the number 

 of eggs, which grow very large and contain much yolk. The 

 ovaries are so small that it seems unnatural to derive them from 

 the large sacs of true Eeptantia ; it is more justifiable to com- 

 pare these gonads with the smaller sacs of Uniporus and other 

 Hoplonemertini that are reduced to one pair per pseudomere, 

 or even to less as in Pelagonemertes and other genera. That 

 the ovaries secondarily migrate into a more central position is 

 shown by B r i n k m a n n in one case ; the young ovaries lie 

 outside the peripheral lateral nerves and when they become 

 older grow inside and become a tube. This tube may bend 

 over the nerves to the inside of them ; but always the origin 

 of the sacs seems to be at the outside of the nerves. The 

 medioventral gonopores of Balaenanemertes, Probalaena- 

 nemertes, Pelagonemertes, and Armaueria may take their 

 origin from the inner leg of such forms, though it may just as 

 well be possible that in Pelagica the more central position of the 

 nerve-cords, as compared with those of other Hoplonemertini 

 for the first time make the displacement of the gonopores to 

 the middle line possible. 



The development of the testes proceeds in two distinct ways. 

 Instead of being present in the middle and hinder parts of the 

 body like the ovaries, they are found only in the anterior 

 part from the brain to the enteron, and in some cases even 



