VAN NAME: SIMPLE ASCIDIANS. 577 
much incurved; open interval turned squarely toward the left in 
all of a number of specimens examined. 
Branchial sac with four well marked folds on each side of the body. 
Of these the first and third are the highest, and the fourth the least well 
developed. Transverse vessels of four orders quite regularly arranged 
according to the scheme: 1, 4, 3, 4, 2, 4, 3, 4, 1, etc. Those of the 
first three orders number forty or more in large specimens. Those 
of the fourth order generally cross without interrupting the stigmata. 
The transverse vessels do not bear conspicuous membranes. Internal 
longitudinal vessels numerous and borne on the interspaces as well as 
upon both dorsal and ventral leaves of the folds. Their distribu- 
tion is, however, difficult to state exactly as there is no way of deter- 
mining at what points the folds should be considered to begin. At 
the summits of the folds the vessels are crowded while on the inter- 
spaces between folds they are separated by the width of four, five, or 
six stigmata (only occasionally more). The vessels are more numer- 
ous on the ventral than on the dorsal leaf of each fold and the vessels 
adjacent to the median dorsal vessel and the endostyle are separated 
from these organs by a considerable interval. The total number of 
vessels in a rather large specimen was as follows : 
mdv. 1 (25) 4 (13) 5 (17) 5 (9) 3 en. 
Smaller individuals have a somewhat less number. 
The stomach has numerous (30 to 35) longitudinal folds, and a long 
pyloric caecum. The intestine forms a rather short wide loop. The 
anus has its margin provided with numerous rounded lobes. 
Gonads (as well as numerous endocarps) irregularly distributed over 
the inside of the mantle on both sides of the body. Well developed 
gonads may number a dozen or more on each side. They are small 
oval sacs tapering at one end to a narrow neck through which the eggs 
are discharged. Beside this neck is the opening of the common sperm 
duct upon a small papilla. The eggs occupy the portion of the gonad 
which lies against the branchial sac, the small pyriform or two- or 
three-lobed testes the portion which lies against the mantle. The 
ducts leading from them are long and do not all unite to a common 
sperm duct until close to the base of the papilla upon which the com- 
mon duct opens. 
It is perhaps worthy of mention that in many specimens of this 
species there are deposits of irregular calcareous granules in the larger 
