ACTINOZOA. 



95 



Order IV. C'tenophora. 



The fourth and last order of the Aftinozoa is that of the C'tenophora, 

 comprising a number of free-swimming oceanic creatures, very dif- 

 ferent in appearance from any of the forms which we liave hitheito 

 been considering, and often placed among the Uydrozoa. They are 

 all transparent, gelatinous, glassy-looking creatures, 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 loco- 



Pig. 5S.— Adult of PleurohracMa rJiododactyla, in a, natural attitude and of the natni :il 

 size. (After A. Agassiz.) c One of the ciliated bands or ctenophores ; t One of the 



motive organs which ai-e known as " ctenophores " (fig. .58, c). In 

 none are there any traces of a corallum or skeleton, and thread-cells, 

 or cells which represent these, are generally present. As the tyjie 

 of the order, we may take PleurohracMa or Cydipjje (fig. 58). The 

 body of Pleurohrachia is transparent, 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 cresceiitic 

 lobes by eight ciliated Iiands or ctenophores, wliich proceed from 

 near the mouth to near the opposite pole of the body. Besides the 



