l,5(i LOWER INVEllTEnnATES. 



WKiymmcXncnX arms. From tliis stage the arms <>railually lengthen, and the spines 

 and suckers develop and increase in number mitil the adult foi-m is reached. 



In some star-fishes the embryo develops directly without ]iassing through a free- 

 swimming stage, and this is esjiecially the case with s)jecies of the southern seas. 



Various adaptations of the si)ines and external membrane ft)rm marsu])ia 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. Echinustvr mrsii does tlie same. 



