16 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
wanderzellen of Hamann, and the amibocytes mb/ri formes of 
Cu6not. They consist, as is usual, of a mass of highly refractive 
spherules — which stain readily with eosin, but do not take carmine 
— imbedded in a small amount of hyaline protoplasm, which encloses 
a spherical nucleus ; this is about 2.6 y in diameter. These cells, 
which, like other amoeboid cells, assume various shapes, measure 
about 8 x 9.3 p, when they take on a spherical form. 
Parallel muscle fibers arranged into the form of hollow cylinders 
(tbl. mu.), which recur~at short, irregular intervals, run outward 
from points in the transverse musculature, through the connective- 
tissue layer and terminate between the calcareous bodies immediately 
beneath the epithelium (Plate 1, fig 5). Each muscle cylinder in a 
relaxed condition runs sinuously and without branching from its 
point of origin to its terminus among the calcareous bodies. At 
their peripheral extremities the fibers of the cylinder generally 
approach one another, come into contact, and form a narrow 
rounded point, to which are attached diverging fibers of connec¬ 
tive tissue. The core of the cylinder appears to consist of the 
homogeneous matrix of the connective-tissue layer. 
The striking resemblance of these muscular tubules to vessels 
which in the Holothuria pedata connect the ambulacra with the 
radial canal led Semper (’68) to the erroneous conclusion that 
they are actually in connection with the radial canal. From a 
study of extensive pieces of the body-wall of young individuals, 
stained, cleared, and mounted in balsam, as well as of sections, I 
have found that the muscular tubules are directly continuous 
with the transverse muscles of the body-wall (Plate 1, fig. 5), and 
I have not in a single instance found them connected with the 
radial canal. The only vessels leading out of the radial canals 
that I have succeeded in finding are in each canal the three 
which run to the tentacles and the three at the tip of the tail. 
. The latter, which are to be described in the account of the 
water-vascular system, are undoubtedly rudimentary ambulacral 
vessels. 
The structure of the muscular tubules suggests that they also 
may be considered to be rudimentary ambulacral vessels, the central 
ends of which have lost their primitive connection with the radial 
canal and have secondarily become united to the transverse muscles 
of the body-wall. On the other hand, they may never have had 
any connection with the radial canal, having arisen directly from 
