1901.] NATUIIAL SCIENCES OF PHILADELPHIA. 689 



served animal it is conspicuous as a small longitudinal slit (fig. 5) 

 about .75 mm. long on either side. It is lined with characteristic 

 glandular epithelium, resembling that found in the head slits 

 (fig. 6)-" 



These facts suggest the possibility that the lateral grooves of 

 ZijgeupoUa may be sense organs that are cither in process of forma- 

 tion, or that have degenerated and lost their sensory character. 



There remains one other interpretation of the lateral grooves, 

 which has been suggested by the presence of the great glandular 

 zone in front of the grooves and the situation of the gonads poste- 

 rior to them. The glandular zone may have a function like the 

 clitellum of the Annelids, and the lateral grooves may be like the 

 grooves found along the sides of the body of an earthworm, and 

 serve to conduct the mucous secretion to the Qgg cells. This last 

 hypothesis could be substantiated only by a careful study of the 

 habits of Zygeupolia. 



4. The Rhynchod.eum. — Immediately behind the tip of the 

 head on the ventral surface may be found a very small opening, 

 the proboscis pore (" Rtisseloffnung "), which is the external open- 

 ing of the rhynchodieum. 



The rhynchodseum is the rather cylindrical cavity that extends 

 through the head from the point of attachment of the proboscis 

 with the body wall, Plate XL, fig. 1, y, forward to the proboscis 

 pore, P.J)., at the tip of the head. It is the path of exit for the 

 evaginated proboscis. 



A transverse section through the rhynchodseum shows that its 

 walls are provided with four stronf? bundles of longitudinal muscle, 

 seen in Plate XLI, fig. 18, Rd.M., and that it is lined with a cili- 

 ated epithelium. This lining is very delicate and liable to be torn 

 away, and usually can be seen only at the most anterior part of the 

 rtiynchodieum. It may persist farther back, but the cilia are 

 mostly broken off in the preparations that have been sectioned. 

 The cilia of this epithelial lining are considerably longer than those 

 of the body epithelium. 



5. Rhyxchoccel axd Proboscis Sheath. — The proboscis, fig. 

 1, P., lies in a spacious cavity, the rhynchocrel. Be, the muscular 

 walls of which form the so-called " proboscis sheath." The rhyn- 

 chocoel is cl jsed anteriorly by the attachment of the proboscis to 



44 



