VAN NAME: COMPOUND ASCIDIANS. 
359 
mentioned vessels, and the musculature is weak. The sphincters of 
the apertures consist of numerous very slender circular bands. From 
the apertures and from the region of the ganglion a rather small 
number of muscle bands, each consisting of but few fibers, run a short 
distance in a posterior or oblique direction, those arising about the 
branchial orifice running straight back, those arising near or around 
the atrial orifice running toward the ventral side of the body. Their 
number and length vary in different individuals, but in most cases they 
Text-fig. 3. — Perophora viridis Verrill. Zooid. X 27. 
are lost long before the ventral or posterior part of the body is reached, 
while the branching vessels of the mantle described above are found 
chiefly on the parts of the body where the muscle bands are wanting. 
The outline of the mantle seen from the side is more or less elliptical, 
but that of the test tapers off more gradually into the pedicle. The 
test is therefore rather thick at the posterior ventral end of the body. 
The branch of the stolon running in the pedicle enters the body of the 
zooid at a point a little above the lower or posterior end of the endo- 
