120 ELEMENTARY ZOOLOGY 



to designate the larvae, but with the knowledge that 

 Bipinnaria are simply young starfishes, and that a Pluteus 

 is simply a young sea-urchin. From these larval stages 

 the adult or fully developed starfish or sea-urchin develops 

 by very great changes or metamorphoses. The Echino- 

 derms have in their life-history a metamorphosis as strik- 

 ing as the butterflies and moths, which are crawling 

 worm-like caterpillars in their young or larval condition. 



Most of the Echinoderms have the power of regenerat- 

 ing lost parts. That is, if a starfish loses an arm (ray) 

 through accident, a new ray will grow out to replace the 

 old. And this power of regeneration extends so far in 

 the case of some starfishes that if very badly mutilated 

 they can practically regenerate the whole body. This 

 amounts to a kind of asexual reproduction. Some- 

 species, too, have the peculiar habit of self-mutilation. 

 1 * Many brittle stars and some starfishes when removed 

 from the water, or when molested in dfny way, break off 

 portions of their arms piece by piece, until, it may be, 

 the whole of them are thrown off to the very bases, 

 leaving the central disc entirely bereft of arms. A central 

 disc thus partly or completely deprived of its arms is 

 capable in many cases of developing a new set; and a 

 separated arm is capable in many cases of developing a 

 new disc and a completed series of arms." In some of 

 the sea-cucumbers "it is the internal organs, or rather 

 portions of them, that are capable of being thrown off and 

 replaced, the oesophagus ... or the entire alimentary 

 canal, being ejected from the body by strong contrac- 

 tions of the muscular fibres of the body-wall, and in 

 some cases, at least, afterwards becoming completely 

 renewed. " 



Classification. The Echinodermata are divided into 

 five classes, viz., the Asteroidea or starfishes, "free 

 Echinoderms with star-shaped or pentagonal body, in 



