The Morphology of Coeloplana, 47 
may be ejected alternately or together. Touching the periphery 
with a needle will often cause one or both of them to be protruded 
a short distance, but I was never able by such means to get the 
whole tentacle thrown out. 
External Appearance. 
Measurements of the size of Coeloplana are not of much value 
in an animal of such great mobility. When fully contracted the 
shape of the body in both species is nearly circular. C. willeyi, in 
such a condition usually measures 1—2 cm across, and C. mitsukurü, 
1 cm or less, — usually about 5 mm. Dorsally, the two species differ 
markedly in color. ©. willeyi varies from pale rose to deep scarlet, 
the intensity of the color in an individual depending of course in 
large measure upon whether the animal is contracted or extended. 
Similarly the smaller species, ©. mitsukurii, ranges from an almost 
pigmentless condition to a deep chocolate brown. The former species 
was nearly always found on red Zostera, while the latter favored 
Melobesia or the bare brown stone. About the periphery there is 
a series of white or whitish-yellow spots or flecks of color (Fig. 1). 
These seem also to be indicated in Korotnerr’s drawing. I have 
been unable to identify them in fixed material or in sections. It 
may be possible that they are sensory in function and sensitive to 
light but I have no evidence on the point. It is worthy of note 
that these spots almost invariably occur opposite a slight notch or 
puckering of the periphery. In both species there is, as in Cteno- 
plana, a rather prominent notch opposite the openings of the ten- 
tacle sheathes. 
The sheath containing the tentacle filaments lies as a loglike 
ridge on either side of the otolith and is made especially prominent 
by being more heavily pigmented than the rest of the body. The 
Sheath terminates exteriorly in a sort of tubelike papilla, a trifle 
back of the peripheral notch mentioned above. The papilla lies 
free above the surface, and when the animal is extended may be 
retracted so as to leave only the opening on the dorsal surface. 
The otolith is comparatively small and in C. willeyi almost 
insignificant in size. It lies in a pit closed by fleshy lips and, in 
the living animal, is frequently difficult to find. 
Next to the tentacles the most prominent thing to be observed 
in the living animal is the network of anastomosing gastric 
canals. These are much less prominent in C. mitsukwrii on account 
