TRANSFORMATION OF PLUTEUS. 199 



the body and processes of the latter assume more 

 and more the appearance of being only appendages 

 to the newly developed animal, until by degrees they 

 entirely disappear, the only part of the Pluteus re- 

 maining as a part of the Ophiurus being the stomach. 

 Before, however, the arms of the Pluteus have entirely 

 disappeared, the feet or retractile suckers have begun 

 to show themselves arranged in a circle around the 

 circumference of the shield-like disc, so that it is able 

 to creep about freely in the sea. 



Shortly before the disappearance of the last rem- 

 nants of the Pluteus, the arms or rays of the Ophiurus 

 are already visible, projecting prominently from the 

 margin of the shield, but consisting as yet only of 

 the outer or terminal joint of the future ray; the 

 moveable spines likewise gradually show themselves, 

 and the characters of the future star-fish begin to be 

 recognizable. Ultimately new segments are slowly 

 added to the rays, making their appearance between 

 the first-formed segment and the margin of the disc. 

 The places where all new segments are formed are in 

 the shield itself, and each successive segment being 

 formed at the base of the ray, is of course, owing to 

 the progressive growth of the animal, larger than all 

 that preceded it. 



Such is the remarkable mode in which the Ophiurus 

 is promoted from its egg condition to its perfect 

 state, after witnessing which, the reader will scarcely 

 be surprised at anything which he may encounter in 

 the way of transmutations of form among the lower 

 animals. 



The Brittle-stars (Ophiocoma, PL IV. fig. 2) are 



