242 ARTHUR E. SHIPLEY. 
alimentary canal (fig. 12). When the introvert is extended, 
the first part of the digestive tube or the cesophagus forms a 
straight tube with smooth walls; when, however, the introvert 
is retracted, the walls of the cesophagus are thrown into a 
number of circular folds with intervening depressions. The 
cells lining this part of the alimentary canal are cubical, and 
thickly beset with cilia. 
Throughout the intestine the lining epithelium is surrounded 
by a layer of connective tissue, which is in its turn covered by 
the peritoneal epithelium ; the connective tissue varies in thick- 
ness in different parts of the tube, but it is especially thick on 
the dorsal surface of the anterior end of the cesophagus: it is 
just here that the single retractor muscle is inserted. 
The cesophagus passes into the descending intestine, whose 
walls are lined by large glandular cells: these have, when the 
intestine is comparatively empty, a columnar shape ; but if the 
intestine is full of food its walls are stretched, and the liuing 
cells become cubical, or even depressed. Owing to the small 
size of the animal it is not possible to wash the food out of 
the alimentary canal, and the nature of the food rendered it 
very difficult to cut satisfactory sections of the walls of the 
alimentary canal. These were in most cases torn ; hence I have 
not been able to settle quite definitely whether the cells lining 
the descending intestine are ciliated or not, but I am inclined 
to think they are. 
The ascending intestine is certainly lined with ciliated cells. 
It is distinguished by the possession of a longitudinal groove, 
which is lined by cells bearing especially long and large cilia. 
A similar groove is described by Mr. E. A. Andrews in Sipun- 
culus Gouldii.'! He states that ‘in it a current of liquid 
passes from the action of cilia, and possibly also of the radiat- 
ing fibres, towards the anus during life.” The absence of this 
groove is the only thing which distinguishes the short rectum 
from the descending intestine. 
1 «Notes on the Anatomy of Sipunculus Gouldii, Pourtalés,” H. A. 
Andrews, ‘Studies from the Biological Laboratory,’ Johns Hopkins Uni- 
versity, Oct., 1890. 
