VAN NAME: SIMPLE ASCIDIANS. 491 
rowest bands, which cross each other in various directions. Radiating 
and circular muscles about the bases of the siphons not strongly 
developed, the radiating bands being of loose structure and not very 
stout, and tapering off quite abruptly at some distance from the origin 
of the siphons. Along each side of the endostyle there are some dis- 
tinct though narrow bands disposed in oblique and transverse direc- 
tions to the course of the endostyle. 
Tentacles moderately numerous and of at least four or five sizes 
and degrees of complexity as regards their branching, which in the 
large tentacles is of the bipinnate type (though a few branches may 
bear incipient branchlets of a third order), while the smallest are 
entirely simple, often mere papillae. Large tentacles comparatively 
few (about six or eight). They vary so much in size that it is probable 
that they represent more than one order. They bear as usual in 
this group broad membranes on the stem and branches; the branch- 
lets have blunt and rounded, though little if at all enlarged, tips. 
Dorsal tubercle large; its orifice C-shaped with the open interval 
to the right; horns not strongly incurved or inrolled. 
Dorsal lamina a broad thick membrane, its border sometimes 
slightly sinuous. 
Branchial sac with rather slight folds on each side, which are ren- 
dered conspicuous by the groups of stout internal longitudinal vessels 
which run along them and by the series of infundibula along their 
summits. The folds being slight, all or most of the internal longi- 
tudinal vessels are visible without disturbing the normal position of 
the folds. These vessels numbered on a medium-sized specimen as 
follows : 
Leftside (5) (5) (4) (4) (4) (2) (2) 
vidv. en. 
Right side (5) (5) (5) (4) (4) (3) (2) 
In large individuals they are more numerous, eight or nine occurring 
on some of the folds. The transverse vessels in most parts of the sac 
are of two orders placed alternately, those of the first order number- 
ing five. Those of the second order are frequently not continuous 
from the median dorsal vessel to the endostyle, but are interrupted 
on the spaces between the folds and limited, except in the ventral 
part of the sac, to the latter; in that part of the sac they may extend 
across the spaces also. In an interval between transverse vessels of 
