100 STARFISH, SEA URCHIN, BRITTLE STARS 



exactly the reverse of tliat in the starfish. The arms of the 

 crinoids are often many times branched and the branches 

 bear sliort, lateral projections called pinnulEe that serve to 

 give the animal a feathery appearance. 



Reproduction and development. — The echinoderms re- 

 produce by eggs, not by bud(Ung, antl the sexes are separate 

 in the majority of species. In one species, at least, the 

 female may be distinguished from the male by a cUfference 

 in color. In this case the female is decidedly l^luish in 

 color while the male is rediUsh brown and presents a 

 marked contrast to the former sex. The eggs and sperm 

 cells are extruded into the water and th(;re the sperm cells 

 find the eggs and fertiUze them. The egg then hatches 

 into a tiny organism, the larva, which has cilia, is free- 

 swimming, and in no way resemlales the adult. The larvse 

 of these animals pass through remarkable changes in 

 their growth to adults and when first discovered, were 

 thought to be distinct species of marine animals and 

 were given various names. For example, the larvaj of 

 sea urchins and brittle stars were called Pluteus, while the 

 larvae of the starfish were called Brachiolaria and Bipin- 

 naria. 



Regeneration of lost parts. — Like the hydra, many of 

 the echinoderms are remarkable for their ability to repro- 

 ihicc ]iarts of the body that may liave been broken or thrown 

 off. Certain of the starfish and manj br-'-flc stars, when 

 molested, will throw off pieces of their arms or sometimes 

 all of their arms. Indeed it is difficult to obtain these par- 

 ticular species whole. Under these conditions the central 

 disk will produce new arms and sometimes an arm will 

 produce a new central disk and the other arms. Stranger 

 still, in some sea cucumbers a part or even all of the all- 



