VAN NAME: SIMPLE ASCIDIANS. 481 
Branchial sac with seven folds on each side, of which all but the 
seventh or most ventral fold are well developed. There are five 
principal transverse vessels extending from the median dorsal vessel 
to the endostyle. On the summit of each fold, in each of the spaces 
marked off by these transverse vessels there are two well developed 
infundibula, many of which divide more or less completely into an 
anterior and a posterior apex. The infundibula of a pair are sepa- 
rated by a short transverse vessel of a second order confined in most 
cases entirely to the fold in which it is situated. Where the infundi- 
bula divide into two apices the latter may be separated from each other 
by short transverse vessels of a third order. The internal longitudinal 
vessels are stout and are confined to the folds except that one vessel 
of the first fold on one side lies a little removed from the base of the 
fold. The vessels number about as follows: 
Left side (5) (6) (7) (6) (5) (4) (4) 
mdv. en. 
Right side (6) (5) (6) (6) (o) (5) (4) 
Stigmata mostly small and short, arranged rather irregularly in 
straight or curved longitudinal rows on the interspaces between the 
folds, their arrangement becoming concentric or irregularly spiral 
on the infundibula. They also occasionally have a tendency to assume 
a spiral or concentric arrangement (indicating the development of 
rudimentary infundibula) on some of the interspaces between the 
folds, usually in the immediate vicinity of one of the large transverse 
vessels, also along the extreme \'entral part of the sac each side of the 
endostyle. Irregular branching vessels lying on the inner surface of 
the sac and crossing usually without interrupting the stigmata are 
extensively developed, especially in the dorsal part of the sac. In the 
spaces each side of the median dorsal vessel they are so numerous as 
largely to cover and conceal the stigmata. They bear small rounded 
papillae on the ends of many of their branches. 
Stomach wall very glandular, with very numerous irregular folds 
and small rounded or irregular projections. The intestine forms a 
loop whose position is mainly horizontal, bending only very slightlv 
upward (dorsally) at the reflected end. The branches of the loop 
approach each other a short distance from the reflected end and run 
nearly parallel for some distance. 
