172 RITTER, (VoL. XII. 
extend so far posteriorly as do the backward extensions of the 
vesicle, 
During its early stages of development the intestine projects 
downward and to the left from the vesicle to which it is 
attached, so as to lie for the greater part in the wide body 
space that surrounds the vesicle (Fig. 29, zv¢., Pl. XIV). As 
development advances, however, it becomes pushed into the 
vesicle, so that ultimately it lies wholly within it, z.e. within 
the atrium in the adult, and by carrying the wall before it as it 
enters the vesicle, it comes ultimately to be wholly enveloped 
by a thin layer of epithelium, which is attached through a thin 
double-layered mesentery to the epithelial lining of the atrium. 
Figs. 29, 30, 32-34, Pl. XIV, illustrate these statements. 
Fig. 29 is from a section that passes through the oesophagus, 
oe., and at the same time cuts the intestine, zzz., in its widest 
part at this stage. 
At this time the intestine lies, as mentioned above, in a 
notch in the ventral side of the vesicle, but projects largely 
into the body space. It has as yet grown very little in length, 
but its lip is already directed forward where it appears in the 
fourth section in front of the one here figured. The distal 
part is considerably smaller in diameter than the proximal, the 
stomach and intestine proper being thus distinguished from 
each other even at this early period. 
The organ grows both forward and outward with advancing 
development, and very soon begins to take on the curved form 
so characteristic of the Ascidian digestive tract. The curva- 
ture is produced by the distal end becoming directed at first 
outward and dorsalward, and then a little later backward. The 
plane of the loop stands at first at an angle of about 45° to the 
horizontal plane. Owing to the backward direction of the tip, 
a section tangent to the loop first appears in a series cut from 
before backward ; and then a few sections farther back the 
loop is wholly passed and a double section of the organ is 
made. This condition is shown in Fig. 32, ves. being the 
rectum, and s¢. the stomach. The long pouch-like appendage 
from the stomach, /. coe., is the beginning of the lacteal coecum 
and duct. It is noteworthy that at this stage it is almost as large 

