COE: NEMERTEANS OF WEST AND NORTHWEST COASTS. 29 



Rhynchodaeum. — Between the attachment of the proboscis in the 

 region of the brain and the external opening on the snout is a nar- 

 row canal, the rhynchodaeum. In most Hoploneniertea, as described 

 on page 28, the esophagus opens into this canal. It is lined with 

 ciliated epithelium, and in certain species of Carinella (Text-fig. 

 2) its anterior portion contains abundant, deeply staining compound 

 glands much like those of the integument. In the hoplonemerteans 

 and heteronemerteans there is a single layer of columnar ciliated 

 cells mthout glands. 



Proboscis sheath. — The proboscis is attached to the tissues of the 

 head on all sides, so that the cavity of the proboscis sheath, the 

 rhynchocoel, is entirely closed from the exterior, and probably has 

 no communication whatever with any of the other cavities of the 



body. 



The rhynchocoel is usually considerably shorter than the body, 

 although in certain genera of hoplonemerteans it reaches the ex- 

 treme posterior end. In Cerebratulus and some other heterone- 

 merteans it is very nearly as long. In other representatives of each 

 of the three principal orders (Carinella, Ejiplectonema, and 

 Taeniosoma, for example) it is scarcely more than one third as 

 long as the body. In Carinella frenata^ and less conspicuously in 

 several other species of this genus, the proboscis sheath enlarges in 

 the nephridial region to form a chamber of considerable size 

 (Text-fig. 5) in which the greater portion of the proboscis is 

 coiled. Posterior to this chamber the proboscis sheath contracts 

 into a narrow tube (re) which passes back for a short distance into 

 the intestinal region, and here the retractor muscle of the proboscis 

 is attached. The enlarged chamber also continues posteriorly for a 

 short distance as a blind sac {re') situated ventrally to the tube in 

 which the proboscis is inserted. In this region therefore a trans- 

 verse section of the body cuts through both portions of the proboscis 

 sheath. When the proboscis sheath is well developed, the greater 

 part of the proboscis is commonly coiled in its anterior third, the 

 posterior portion being filled mainly with the rhynchocoel fluid. 



Only in the genus Drepanophorus are there any appendages to 

 the rhynchocoel, which in this case has paired, tube-like diverticula 

 throughout the greater part of its length. These are metamerically 

 arranged, the pairs of diverticula corresponding in the intestinal 

 region with the pairs of intestinal pouches, which they border dor- 



