638 



GERARDA STIASNY-WIJNHOFF 



structure of the digestive system and the arrangement of the 

 diverticula of the proboscis sheath separate them. 



The most interesting feature seems to be the structure of the 

 cerebral organ that is so highly developed in the Eeptantia. 

 This sense organ consists in the Monostilifera (Text-fig. 12, a) 

 of three different parts : a channel, a ganglion, and glands. 

 These are joined together to a more or less rounded organ with 

 its own neurilemma. In the Reptantia the same constituents 

 are present, but as a rule the different parts are more free from 

 each other and partly lie outside the rounded circumference 

 of the organ, as in Drepanophorus cerinus and wil- 



Text-fig. 11. 



Schematic longitudinal section of the digestive tract of S i b o g a 

 nemertes weberi after transverse sections. 



ley anus (14, 15) and in Uniporus (3). Moreover, the duct 

 that leads from the cephalic furrows into the cerebral organ 

 bifurcates in the organ ; one part gives rise to a more or 

 less spacious sac, characteristic of Reptantia, and the other 

 part ends as a narrow duct in the glandular portion of the 

 organ (Text-fig 13). Both sac and glandular tube can lie 

 embedded in the body parenchyma. In Siboganemertes there 

 is no bifurcation of the cerebral canal (Text-fig. 12, h). When 

 the channel gets to the ganglion two small bunches of glands 

 open into it which lie quite free. The epithelium is sensory 

 and never gets glandular. The channel is as primitive as 

 possible ; it turns backward at the contact with the ganglion 

 and at its end bends upward and forward on its first part, 

 where it ends blindly. This is the most primitive cerebral 



