62 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOCxY. 



pits, and in several related genera but a single one. In some cases 

 the ducts fi'om the cephalic glands enter an apparently homologous 

 pit, as in Tap:niosoma, Geonemertes, and other genera of both the 

 higher oixlers. In such cases this frontal pit often becomes very 

 deep, and may penetrate the tissues of the head back nearly to the 

 brain region (Geonemertes). It not only serves as a duct for the 

 secretions of tlie cephalic glands, but retains a specialized sensory 

 epithelium. 



Cephalic soisot'ij jyits. — In Carinoma mutabilis^ as well as in (\ 

 tremaphoros (Thompson, :00, p. 627) and C. arwja?«f?i (Bergendal, 

 :03, p. 610, and : 04, p. 44), a number of small sensory pits are sit- 

 uated in the median line on the dorsal surface of the head. They 

 are apparently homologous with the fi'ontal sense organs and 

 frontal pits of many of the Heteronemertea and IIo})lonemertea, 

 as described above. Their function is doubtless similar to that of 

 the cerebral sense organs in other Paleonemertea. Their number 

 is usually from 6 to 12, and they are placed at irregular intervals 

 between the brain and the tip of the snout. In structure each 

 sense oi'gan consists of a small cup, or hollow sphere, of sei]sory 

 cells situated at the base of the integument and closely pressed 

 against the underlying basement membrane. 



These sense organs may open widely at the surface or become 

 well separated fi'om it, according to the state of contraction of the 

 parts. In the latter case they are connected with the exterior by 

 narrow canals. The sensory cells are provided with long cilia and 

 are apparently connected with the brain by one or more nerves from 

 the dorsal commissure. In (\tremap>horos and in C armandi such 

 sense organs are comparatively well developed, while in C. mutabilis 

 they are so very inconspicuous that they were overlooked in my 

 original description. 



They appear to lie j^roAided with special muscular fibers, and 

 can doubtless be opened and closed to some extent by the muscular 

 contractions, much as is the case with the lateral sense organs. 



Reproductive Organs. 



All the nemerteans as yet known fi-om the Pacific coast, with the 

 exception of Tetrastemma caecum^ which is probably i)arasitic, and 

 the fresh water Stichostemma, are of separate sexes. Very few 



