ACTINOZOA. . gI 
sac-like stomach, which opens inferiorly directly into the body- 
cavity (fig. 32, 4), and communicates with the outer world 
through the mouth. A nervous system has not been shown to 
exist in any of the Actimozoa except the Ctenophora, and perhaps 
some of the sea-anemones, and in none are there any traces of 
a circulatory system. Distinct reproductive organs are always 
present, and true sexual reproduction occurs in all the members 
of the class. In a great many forms, however, of the Acéznozoa, 
we have composite organisms or colonies, produced by a process 
of ‘‘continuous” gemmation or fission, the zodids thus originated 
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. 
YU Ph i) Nw \S 
D 
Fig. 32.—A, Actinia mesembryanthemtum, one of the Sea-anemones (after John- 
ston) ; B, Section of the same, showing the mouth (a), the stomach (4), and the 
body-cavity (c). 
remaining attached to oneanother. In these cases—as in most 
of the corals—the separate beings or zodids thus produced are 
termed “ polypes,” the term ‘‘polypite” being restricted to the 
Hydrozoa. Inthe simple Actznozoa, however, such as the sea- 
anemones, the term “‘ polype” is applied to the entire organism, 
as consisting of no more than a single alimentary region. It 
follows from this, that the entire body, or “ actinosoma,” of any 
Actinozoon, may be composed of a single polype, or of several 
such, produced by budding or cleavage, and united to one an- 
other by a common connecting structure or coenosarc. Most of 
the Actinozoa are permanently fixed, like the corals; some, like 
the sea-anemones, possess a limited amount of locomotive power; 
and one order, the Czexophora, is composed of highly-active free- 
