140 ECHINODERMATA. 



but mere rudiments of what we have seen in Comatula, may still 

 assist in locomotion, or perhaps may contribute to retain the prey 

 more firmly when seized by the arms. The rays themselves are 

 composed of many pieces curiously imbricated and joined together 

 by ligaments, so that they are, from their length and tenuity, ex- 

 tremely flexible in all directions, and serve not only for legs adapt- 

 ed to crawl upon the ground, but are occasionally serviceable as 

 fins, able to support the animal in the water for a short distance 

 by a kind of undulatory movement. The body, or central disc, 

 is beautifully constructed, being made up of innumerable pieces ac- 

 curately fitted together. The mouth occupies the centre of the 

 ventral surface, and is surrounded by radiating furrows in which 

 are seen minute apertures that give passage to a set of remark- 

 able prehensile organs, to be described hereafter : these are calcu- 

 lated to act as suckers, and so disposed as either to fix the body of 

 the animal, or to retain food during the process of deglutition. 



Fig. 60. 



Leaving the Ophiuri, we are led through a long series of almost 

 imperceptible gradations to animals apparently of most dissimilar 

 structure. The star-fishes (Asterias) (Jig. 65) form the next step : 



