REMARKABLE SPECIES OF ECHIUROIDS. 43 



at other places are joined to one another by means of some short 

 processes, leaving mesh-like spaces between them. The cytoplasm 

 of the cells is deeply stained by eosin or erythrosin and shows 

 a finely granular structure. The most deeply situated cells of 

 the layer are not infrequently provided with longer processes 

 than those more superficially situated, and that often in a less 

 number, — thus approaching the form of the ramified mesenchyme 

 cells in the deep parts of the proboscis. On the dorsal side of 

 the proboscis, the continuity of the peripheral mesenchyme 

 layer is much broken as seen on sections, on account of the 

 presence of the club-shaped unicellular glands (figs. 43 and 40). 



RiETSCH ('86) has described from Bonellia minor and 

 Thalassema neptuni a subdermally situated layer of " cellules 

 ganglionaires," which occupy a position outside of the dermal 

 muscle layers and which stand in direct connection with epider- 

 mal cells by means of fine processes. Now, the above described 

 peripheral mesenchyme cells are not without resemblance to the 

 " cellules ganglionaires." Nevertheless, it seems not warranted 

 to directly homologize the two, since the former are situated 

 inside, instead of outside, the dermal muscular layers. Moreover, 

 in T/h. kenioides the epidermis of the proboscis, unlike that of 

 the body proper, is found to be everywhere separated from the 

 underlying tissue by a distinct limiting membrane, and under no 

 circumstance could a direct plasraic connection be demonstrated 

 to exist between the two tissues. 



In two ventral regions of the proboscis, the layer of the 

 peripheral mesenchyme is specially thickened internally into a 

 pair of massive, longitudinal bands (mnrked with + in fig. 43), 

 which on transverse sections present . a somewhat triangular 

 outline and are conspicuous on account of an unusually dense 



