NEMBRTBA ENOPLA 657 



development supposed by Brink ma nn seems to have 

 taken place in the reverse direction ; what he calls highly 

 reduced, I call primitive, and vice versa. 



This disagreement does not extend to the nephridial 

 system; for this is present in all Nemerteans without 

 exception that do not belong to the Pelagica. That it has 

 not yet been found in Prosadenoporus must partly be due to 

 the highly developed head-glands that extend into the nephri- 

 dial region, partly to the smallness of the canals or the preserva- 

 tion. As all Platyhelminths possess a well-developed nephridial 

 system, we are obliged to explain its absence in the Pelagica 

 by reduction. In Siboganemertes nephridia are present, but 

 of a type that differs from that of the Eeptantia. A large 

 efferent duct is present at each side, extends behind the real 

 nephridium, and has a more caudal, lateral mouth. The 

 nephridia lie at the side of the dorsal brain-lobes and the 

 cerebral organs, and just behind these obtain their greatest 

 development. The ducts open laterally behind the end of the 

 pyloric tube. This type is known from primitive Anopla, 

 a well-localized system of canals with a long efferent duct, 

 quite different from the other types of nephridia that extend 

 through the whole body in the same way and have one or more 

 short ducts. In the Eeptantia also it is much less circumscribed, 

 extends as a rule from the end of the brain along the stomodaeal 

 tract, and has one efferent duct that can take its origin in any 

 part of the system and opens directly to the exterior. Our 

 knowledge of Monostilifera is as yet too incomplete to under- 

 stand the value of these facts. 



The gonads, however, seem to be much more interesting. 

 The only individual of Biboganemertes happened to be a male 

 with well-developed testes, a fact of the greatest importance, 

 as the Pelagica exhibit an extraordinary feature in the position 

 of these glands that is characteristic of the group. 



As a rule the gonads lie, be they V or o^, in the intestinal 

 region in armed and unarmed Nemerteans. The only exception 

 are the testes of the Pelagica that never are developed in this 

 region, and always lie before it, directly behind, at the side of, 



NO. 268 X X 



