VAN NAME: SIMPLE ASCIDIANS. 
573 
confined to the folds or lying so close to their bases as to make it evident 
that they should be counted as belonging to a certain fold. Between 
the second and third folds, however, there is usually one stout vessel 
on the interspace nearly midway between the folds on each side of the 
Text-fig. 37. — Tethyum molle (Stimpson). X 5.3. 
sac. Counting all the other vessels as belonging to the nearest fold, 
the scheme in several specimens studied was about as follows : 
mdv. (8 to 10) (4) 1 (8 to 11) (6 to 7) en. 
Transverse vessels of three orders, the smallest merely crossing the 
stigmata and incomplete in many parts of the sac. About thirty 
rows of stigmata in a good-sized specimen; 12 to 25 stigmata on the 
interspaces between folds in the widest part of the sac. 
Stomach rather broad, well differentiated from the esophagus and 
intestine, with a small curved pyloric caecum and about 25 longitudi- 
nal folds in its wall. Intestinal loop small; anus with a sinuate 
margin, or somewhat two-lipped. 
Gonads phial-shaped, tapering to a short neck with a terminal 
aperture for the discharge of the eggs at the dorsal end. Testes small 
piriform or somewhat lobed, occupying the part of the gonad adjacent 
to the mantle. Their ducts embrace the ovary (which occupies the 
part of the gonad adjacent to the branchial sac) and unite to a com- 
mon sperm duct running along the free side of the ovary (next to the 
branchial sac) and opening on a papilla at the side of the neck of the 
gonad. Gonads placed so that their orifices are directed toward the 
base of the atrial siphon, those of the left side usually four in number, 
situated anterior to the alimentary tract. On the right side, the 
gonads are more numerous, usually six in number, sometimes seven. 
Described by Stimpson (1852) from specimens dredged off Cheney's 
Head, Grand Manan, N. B., in 10 fathoms, sandy bottom. Rede- 
