358 PTEROPODA. CLIO. 



inconsiderable, yet the number of individuals which associate 

 together in shoals is often enormous, so that the sea appears 

 literally alive with them. Some of them 

 are possessed of a shell; whilst others 

 are unprovided with such a protection. 

 Where it exists, it is very light and deli- 

 cate ; and it seldom covers more than 

 the posterior half of the body (Fig, 552). 

 In one beautiful little Mollusk, the Cym- 

 bulia, it has the form of a slipper ; from 

 the large opening of which, the wings or 

 fins are put forth. The head of these 

 animals is usually prominent, possess- 



FIG. 552. HYAL.*EA. , * 



ing eyes and sensory tentacula; and 

 their internal organisation is of a very complex nature. 



900. The Clio (Fig. 551) is one of the best-known genera of 

 this class ; and its general aspect conveys a good idea of that of 

 the whole group. One species of this genus, the Clio lorealis, 

 abounds in the Arctic seas ; presenting itself in such vast num- 

 bers, that, when the weather is calm, the surface appears covered 

 with them for miles together; and an analogous species, the 

 Clio australis, appears to be equally abundant in the polar 

 regions of the southern hemisphere. These animals are well 

 known to the whale-fishers and others, as whales' food, being 

 among the chief articles on which that monster, the largest 

 existing animal, is supported. It has been asserted that the 

 sea is sometimes so glutted with the Clios, that the Whale can- 

 not open its mouth without ingulphing thousands of them. The 

 chief point of special interest in the structure of the Clio, is the 

 conformation of its organs for the capture and mastication of its 

 food. The six tentacula, which are seen to project from the 

 head, and which appear at first sight to be merely fleshy append- 

 ages, are in reality instruments of prehension, most elaborately 

 constructed. Each of these six appendages, when examined 

 attentively, is seen to be of a reddish tint ; and this colour, under 

 the microscope, is found to be dependent upon the presence of 

 numerous minute isolated red points, distributed over its surface. 



