ASCIDIA. 55 
ALIMENTARY CANAL. 
The cesophagus is a short, narrow, curved tube which 
leads ventrally to the stomach—a large, thick-walled 
organ, lying on the left-hand side of the branchial sac, 
imbedded in the body-wall and projecting into the atrium, 
(as shown in fig. 4, Pl. II.). From the other (ventral) 
end of the fusiform smooth-walled stomach arises the 
intestine, a long serpentine tube which ends by opening 
into the dorsal or cloacal part of the atrium, from which 
the undigested portions .of the food are carried to the 
exterior through the atrial aperture, by the water current. 
The intestine is curved so as to form two loops (PI. IL., 
fig. 4), a first between the stomach and intestine, open 
posteriorly, and in which the ovary lies; and a second 
between the intestine and rectum, open anteriorly, and in 
which the renal vesicles lie. The external convex edge of 
the intestine is thickened internally to form the ‘‘typhlosole,”’ 
a large pad which runs along its entire length (Pl. IL., figs. 
2 and 4, ty.), reducing the lumen to a crescentic slit. 
The walls of the stomach are glandular; and, in addi- 
tion, a system of delicate hyaline microscopic branched 
tubules with dilated ends (the ‘“‘refringent organ’’), 
which ramifies over the outer wall of the intestine and 
communicates with the cavity of the stomach at the 
pyloric end by means of a duct, is possibly a digestive 
sland. There is in Ascidia no separate large gland to 
which the name ‘‘liver’’ can be applied as in some other 
Tunicata (e.g., Molgula). Over these viscera, on the left 
side of the body, the body-wall is thin and gelatinous, and 
has usually no muscle fibres visible. 
The wall of the alimentary canal, throughout its length, 
consists of an epithelial lining (endoderm), a thick layer 
of highly vascular connective tissue, and, over that, the 
flattened epithelium lining the peribranchial cavity. The 
