VAN NAME: COMPOUND ASCIDIANS. 
393 
number 12 in vounii' zooids, and are then of two sizes arranged alter- 
nately. Fully adult zooids have 12 more still smaller tentacles between 
the others, or 24 in all. 
The branchial sac has four rows of stigmata with from 12 to 14 
stigmata on each side in the anterior rows, but only about ten in the 
last row. The transverse vessels are provided with a few muscle 
fibers and a band of muscle fibers runs along each side of the median 
dorsal vessel. There are three dorsal 
languets, which, as above noted, ap- 
pear to arise directly from the median 
dorsal vessel, though perhaps more 
from its left than from its right side, 
so that their bases are in contact with 
the left transverse vessels. The stom- 
ach is oval and smooth-walled. The 
folds in the stomach wall mentioned 
by Professor \'errill must evidently 
have been caused by the contraction 
incident to preservation. The intes- 
tinal loop is twisted through about 
180° on its vertical axis, bringing the 
stomach to the dorsal side, and also 
bent to the right, so that the repro- 
ductive organs appear to have a posi- 
tion posterior to the intestinal loop. 
There is a distinct constriction or 
valve in the intestine near the point 
where it begins to ascend. 
The testis is divided into from five 
to nine or ten pyriform bodies placed 
radially, with their apices close together and more or less posteriorly 
directed with reference to the axis of the body. Very short connecting 
ducts arising from their apices unite to form the common spertn duct 
or vas deferens, which has a nearly straight course to and then 
parallel with the rectum. Near its origin it often expands into a large 
spindle-shaped seminal receptacle. Generally the divisions of the 
testis are completely or almost completely separated from each other, 
but there seem to be individual differences in this respect. When 
the testis becomes large, the parts become closely crowded together, 
Text-fig. 20. — ■ LissocUnum aureum 
Verrill. Zooid. X 42. 
