The Morphology of Coeloplana. 51 
whole ciliated surface I cannot say. In the living animal the cilia 
are very evident over the entire ventral surface. 
Scattered over the basement membrane and through the adjacent 
parenchyma, and showing through the outer layer of epithelium, are 
numerous irregular, branching, pigment cells. These cells, so 
far as I have been able to make out, are confined to the dorsal 
surface. There is great variation in pigmentation, such cells being 
practically absent in some specimens. The substance of the cells is 
granular, and the color appears to be due to a deposit of some 
highly refractive material in tiny spherules. These are very likely 
similar to the iridocytes in the integument of fishes. The pigment 
cells are sometimes (but rarely) found among the epithelial cells 
proper. In nearly all cases they are found among the connective 
tissue and muscle cells that underlie the true epithelium. They are 
of course most numerous in C. mitsukurii and in both forms are most 
noticable at the bases of the dorsal tentacles and over the tentacle 
sheath. In C. mitsukurii they are very thickly scattered through 
the tissue of the fringed dorsal tentacles themselves, but are absent 
in the unbranched dorsal tentacles of C. willeyi. 
The basement membrane is rather thick and is intimately 
connected with the connective tissue and muscle cells of the 
parenchyma. 
b) Gastrovascular system. 
General organization. 
The mouth is large, roughly quadrangular or four lobed and 
lies immediately beneath the sense organ. It opens into a capacious 
pharynx or stomodaeum, the walls of which are thrown into a great 
number of folds. Plane section shows that the pharynx is not 
compressed in either plane but is approximately square in shape, 
the wall projecting into the cavity from four sides, in the tentacular 
and transverse planes. Kowanevsky describes the mouth of Coelo- 
plana as leading directly into the stomach (infundibulum?) without 
the intermediate development of a pharynx, but the observation is 
a questionable one as he evidently did not preserve and section his 
specimen. The complicated pharynx in ©. mitsukwriüi and C. willeyi 
is, in the living animal, extremely difficult to make out except under 
the most favorable circumstances, but it is very prominent in fixed 
and stained material. 
