VAN NAME: SIMPLE ASCIDIANS 487 
Principal transverse vessels of the sac five in number. Short trans- 
verse vessels of the second order (confined, except in the ventral 
region, to the folds themselves and not extending on to the interspaces) 
occur midway between the principal ones, and in the intervals still 
smaller and shorter vessels of a third order are present, especially in 
large specimens, their presence depending upon whether or not the 
infundibula fork or divide a second time, as described just below. 
Stigmata short and arranged on the interspaces between the folds 
in longitudinal rows, which, as a transverse vessel is approached, 
curve toward and extend on to the nearest fold. The summit of 
each fold is formed by a series of large low infundibula, only one gen- 
erally occupying each of the spaces marked off by the principal trans- 
verse vessels, and on these infundibula, the stigmata gradually assume 
a concentric and irregularly spiral arrangement. Each infundibulum 
divides into two cones (a posterior and an anterior) separated by a 
short transverse vessel of the second order, and some of them (in very 
large individuals most of them) divide a second time so that there is a 
series of four small cones along the summit of the folds between each 
principal transverse vessel. On the cones the stigmata become very 
narrow and are separated only by slender vessels. These infundibula 
are bridged over by the internal longitudinal vessels running along 
the summit of the fold. Infundibula do not develop elsewhere and 
only rarely is there any tendency to a spiral arrangement of the stig- 
mata except on the upper parts of the infundibula just described. 
Fig. 22 shows the arrangement of the folds, vessels, and stigmata 
in an adult individual of medium size. In very large individuals 
both the longitudinal and the concentric or spiral rows of stigmata 
will usually be found more numerous; the stigmata remain short even 
in the largest specimens. 
The stomach wall is either very delicate or, in the specimens ex- 
amined, had been injured by digestion after death, so that its structure 
could be made out only imperfectly. The wall of the proximal part 
of the organ has many deep plications which are more or less irregular 
and variable in length and direction. In one specimen at least, these 
folds appeared to form a rather conspicuous glandular mass on the 
posterior aspect of the stomach. The intestine forms a loop whose 
sides are separated fairly widely for a short distance near the reflected 
end but elsewhere are close and overlapping. The whole loop forms 
a somewhat angular curve, widely open dorsally. Margin of anus 
sinuate. 
