STARH'ISH, MA-UnOBlNS, AND SEA-CUOUMBEES. 63 



barrel-shaped creature, which usually has ciliated bands or 

 zones around its body; the Holothurian grows up in it, in 

 nearly the same way as the starfish grows from tlie larva. 



On review, we see that the EcMnoderms differ from the 

 worms in the body being very distinctly star-like or radiated j 

 that the skin is usually filled with solid, limestone plates, 

 forming a shell ; that they all have a tube-like digestive 

 canal, which lies loose and free in the body-cavity; that in 

 the sea-urchin there are five teeth for cutting up the food; 

 that EcMnoderms can see and smell, and that most of them 

 pass through a metamorphosis. They are very complicated 

 animals compared with a sponge, a polyp, or even a jelly- 

 fish, having a body-cavity, blood-vessels, and often gills. 



Fia. 57.— Sea-oucumber (Synapta). A, larva. B, Young farther advanced, with 

 the Synapta (/. d) growing within. C, young become free (after Miiller). 

 D, adult Synapta. (Kingsley del.) 



Classes of Echinodbrmata. 



1. Body mounted on a stalk CrinoicUa (stalked starfish). 



2. Body with five arms; free Asteroidea (starfish, etc.). 



3. Body spherical, with long spines EcMnoidea (sea-urchins). 



4. Body elongated; skin soft, hardened 



by minute plates Holothuroidea (sea-cucumbers). 



LiTBRATUKB. — Q. J. Bomanes : Jelly-fish, Star-fish, and Sea-- 

 urchins, 1 885. — J. Miiller : Seven Memoirs on the Larvte and Develop- 

 ment of Echinoderms. Berliji, 1846-54. — A. Agassiz: Embryology 

 of the Sliirfish, 1864, and Seaside Studies. — E. Metschnikoff : Studien 

 ilber die Entwickelungsgeschichte der Echinodermen uud Nemer- 

 tiuen. St. Petersburg, 1869.— S! Liidwig : Morphologische Studien 

 an Echinodermen. Leipzig, 1877-78. 



