2 
Transactions of the Royal Microscopical Society. 
posterior sucker. For its examination a power of five or six 
hundred is desirable, although its general features may be studied 
with a Yoths objective. Its surface is studded with considerable 
regularity by minute, upstanding, firm elevations resembling cells, 
but apparently quite structureless. Beneath this layer and looking 
like a changed condition of its deepest part, are granules of uniform 
size and symmetrical arrangement, in rows corresponding with and 
transverse to the longitudinal axis of the body ; the latter being 
most marked, gave a striated appearance, reminding one of striped 
muscle ; at other times by a slight alteration the resemblance to the 
markings of a Pleurosigma was most striking. Beneath this layer 
is a thin structureless membrane, by a reflexion of which a space 
near the mouth is cut off' from the main body ; this space, together 
with the general interior of the creature, is occupied by a granular 
protoplasmic substance mixed with clear droplets. The mouth has 
three lips, and leads into a slight depression or pharynx, often 
deepened by retraction into the space above mentioned. On the 
middle of the ventral surface is an oval sucker, in size about a third 
the diameter of the body: transverse striation is very distinct in its 
central depressed part. Behind the sucker a clear, elongated, 
curved space was frequently seen in the interior of the body, which 
space, after remaining some time, appeared suddenly to collapse. 
On the dorsal surface a little in front of the sucker was situated a 
somewhat stellate space, over which the surface of the body was 
depressed. These spaces perhaps represent a rudimentary water- 
vascular system. Near the sucker, in all specimens examined, were 
three minute spherical concretions of unequal size, moving freely in 
the general substance ; they were the only parts that showed double 
refraction under polarized light, under which they were very con- 
spicuous. On the under surface near the mouth was an elevation 
with a notch at its posterior margin ; at the attached end close to 
the spheres were two diffused masses of greater opacity and 
granularity. 
