156 LOWER INVERTEmiATES. 



unsymmetricMl arms. From this stage the arms uradually lengthen, and the spines 

 and Slickers de\elop and increase in number until the adult form is reached. 



In some star-fishes tlic emlirvo (lcvcl()j)s directly without jiassiiig through a free- 

 swimming stage, and this is esjiecially the case with siiccies of the southern seas. 



Fifi. 138. — -Zicisiiii/ri caronata. 



Various adaptations of the spines and external membrane form marsupia for the 

 protection of the young while attached to the parent. A large species of Asterias, 

 dredged in Stanley Harbor, formed a shelter for its young by drawing its arms 

 inwards and forwards over the mouth. Echinaster sarsil does the same. 



