ACTINOZOA, cept 
which are found near the surface in the open ocean, swimming 
rapidly by means of bands of cilia. The cilia are arranged in a 
series of transverse ridges, which are disposed in longitudinal 
bands, the whole constituting locomotive organs which are 
known as “ctenophores.” In none are there any traces of a 
corallum or skeleton, and thread-cells are asserted to be univer- 
sally present. As the type of the order, we may take one of our 
commoner forms, which is known by the name of Pleurobrachia 
or Cydippe (fig. 40). The body of Pleurobrachia is transparent, 
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Fig. 40.—Ctenophora. Pleurobrachia pileus. 
colourless, gelatinous, and melon-shaped, and exhibits two 
poles, at one of which is placed the mouth. The globe-like 
body is divided into a number of crescentic lobes by eight 
ciliated bands or ctenophores, which proceed from near the 
mouth to near the opposite pole of the body. Besides the cilia 
there are two very long and flexible tentacular processes, which 
are fringed on one side by smaller secondary branches. The 
tentacles arise each from a kind of sac, one placed on each side 
of the body, and they can be instantaneously and completely 
retracted within these sacs at the will of the animal. The 
mouth of Pleurobrachia, opens into a spindle-shaped digestive 
sac or stomach, which in turn opens below into a wider and 
shorter cavity termed the ‘funnel ;” from this there proceed in 
the axis of the body two small canals, which open at the oppo- 
site pole of the body. The funnel communicates with a com- 
plicated system of canals, which are ciliated internally, and are 
