i86 coE 



tissues of the head on either side of the anterior end of the rhyncho- 

 daeum. The retina faces ventrally. The remaining ocelli are much 

 simpler in structure. 



In internal organization this species shows a close resemblance to 

 L. rubescens^ and hence a considerable departure from the typical 

 species of the genus in many details of structure. The close similarity 

 in many anatomical features between these two species and Zygeu- 

 folia^ as described by Miss Thompson (1902),^ is very striking, and 

 serves to unite this genus more closely to the other members of the 

 Lineid^e. 



Proboscis. — Proboscis sheath does not extend to end of body. 

 Proboscis attached to dorsal wall of sheath at the posterior end of the 

 esophageal region, and only a few sections in front of the intestine, by 

 a powerful retractor muscle. In this same region the circular muscles 

 of proboscis sheath extend ventrally to surround the esophagus with 

 a rather thick layer of circular muscles. The fibers are connected to 

 some extent with the main circular muscular layer of the body walls 

 by a crossing of fibers immediately above the proboscis sheath. This 

 recalls the great thickness of the inner circular muscles found in this 

 same region in Carittoma. A similar condition has been described 

 iox Micrura alaskensis (Coe, 1901),^ and Miss Thompson (1902)' has 

 recently described for Zygeupolia litioralis and Micrura cceca a well- 

 defined inner circular layer in this region, and has shown its apparent 

 homology with the inner circular muscular layer of Carinella^ Cari- 

 noma and other Paleonemerteans. 



This localized inner muscular layer doubtless serves the double pur- 

 pose of holding the proboscis sheath, with its attached proboscis, 

 firmly in place among the other tissues, and of providing a strong 

 annular constriction between the esophagus and intestine. By the 

 action of this sphincter, food materials, having entered the intestine, 

 may be prevented from returning to the esophagus. Furthermore, 

 the esophagus may under some circumstances act as a respiratory 

 organ, as described by Wilson (1900)* for Cerebratuhis lactcus^ and 

 as I have observed in other species, and in this case the muscular con- 

 striction will prevent the water from passing back into the intestine. 



The muscular walls of the proboscis consist of the outer longitudinal 



and inner circular layers only. The inner longitudinal layer, which is 



iProc. Acad. Nat. Sci. Philadelphia, 1901, pp. 657-732. 



2 Preceding article, p. 72. 



^ Loc. ct't., p. 667. 



* Quart. Journ. Micr. Sci., XLiii, p. 109. 



