2Ö2 THE GENERA OF NEMERTEANS. 



about six times as long as wide separates the anterior and 

 posterior region of the proboscis. The same constriction 

 — however of a different character — is found in Valen- 

 cinia and Polia , it has disappeared in the Lineidae, whereas 

 in the armed species is has become more strongly differen- 

 tiated and is represented by the muscular bulb in the 

 proboscis which contains the stylet and the styliferous 

 vesicles. 



The interior of the proboscis appears to be divided into 

 compartments by numerous transverse, thin, ring-shaped ridges 

 which seem to offer different aspects in the three suborders 

 proposed above. Whereas in the Schizonemertini they are 

 visible throughout the whole length of the proboscis at 

 equal and comparatively short distances , they make their 

 appearance in the Palaeonemertini only in the anterior part, 

 which it situated before the above mentioned constriction. 

 In the suborder of the Hoplonemertini they seem to have 

 disappeared altogether. Both here and in the Palaeonemer- 

 tini there is a characteristic granular appearance in the 

 posterior half of the proboscis behind the constriction , 

 which is again absent in the Schizonemertini , where the 

 segmented character of the anterior part in uninterruptedly 

 maintained throughout the whole length of the organ. 



A posterior lobe of the cerebral ganglion communicating 

 by a ciliated duct with the exterior could not yet be 

 detected in Carinella or in Cephalotrix ; it is however pre- 

 sent in Valencinia and Polia and in both very intimately 

 connected with the anterior lobes. In both these genera 

 the exterior opening of the ciliated canal is small, but 

 whereas in Polia a transverse groove in the epiderm with 

 numerous smaller grooves perpendicular to the first and 

 all strongly ciliated seem to lead to this opening, such 

 complications are absent in Valencinia. They are again 

 met with in the armed genera Amphiporus and Drepano- 

 phorus where they exactly resemble those of the unarmed 

 Polia. Here however the posterior lobes have become more 

 detached from the ganglion , only communicating with it 



Note» from the Leyden IVIuseum. 



