VAN NAME: SIMPLE ASCIDIANS. 583 
Largest specimen in the collection, about 25 mm. high. Station 
2449. 
Right side 1 (19) 2 (10) 2 (13) 3 (11) 1 
V2dv. en. 
Leftside 1 (30) 2 (7) 3 (11) 3 (7) 1 
Small specimen 8 mm. high. Stations 53, 54. 
Right side 7ndv. 1 (13) 2 (5) 1 (8) 1 (3) 1 eri. 
Total number of vessels greater in large than in small specimens. 
The vessels are confined to the folds except that one vessel dorsal and 
one or two ventral to each fold lie on the interspace, removed a varying 
distance from the base of the fold. That these really belong to the 
groups on the folds is shown by their often approaching and joining 
the groups on the nearest folds as one end of the sac is approached. 
In young individuals all or nearly all the vessels may lie upon the folds. 
The stigmata are numerous and in large individuals 15 to 25 of them 
often intervene between internal longitudinal vessels on the inter- 
spaces between folds, but these numbers vary much according to the 
number and position of the above mentioned outlying vessels. The 
transverse vessels are of four sizes, the smallest merely crossing the 
stigmata. 
The stomach is oblong, of moderate size, with a very small or rudi- 
mentary pyloric caecum and twenty or more longitudinal folds. The 
intestinal loop is narrow and generally so bent that the intestine lies 
close against the stomach for the whole length of the latter organ, 
but the exact course and form of the intestinal loop are very variable 
and often influenced by the indentations of the body caused by the 
pressure of external objects. The margin of the anus is reflected and 
nearly plain. 
The gonad had three nearly parallel obliquely or nearly horizontally 
placed branches in all the specimens examined. The details of its 
structure could not be very well made out in the specimens studied. 
In each branch the ovary appears to occupy a central position and 
the testes seem to border it as is usual in this family. In the typical 
D. aggrcgata the gonad usually has five branches. 
Verrill (1871a) described this species from small specimens from 
Eastport, Me. The types were not found in the collection, but there 
were other specimens which he had labeled C. pulchclla. Later, 
however, he seems to \\2i\e become doubtful whether this was really 
