THE LIFE CYCLE 



271 



urchins, show a similar metamorphosis, except that there is 

 no plnteus stage, the true star-fish-shaped body forming, 

 within and at the expense of the first larval stage, the ciliated 

 free-swimming stage. 



A young crab just issued from the egg (Fig. 151) is a 

 very different appearing creature from the adult or fully 

 developed crab. The body of the crab in its first larval 

 stage is composed of a short, globular portion, furnished with 

 conspicuous long spines and a relatively long, jointed tail. 



FIG. 150. Metamorphosis of sea-urchin. Upper figure the adult, lower ngure tht 



pluteua larva. 



This is called the zoea stage. The zoea changes into a stage 

 called the megalops, which has many characteristics of the 

 adult crab condition, but differs especially from it in the 

 possession of a long, segmented tail, and in having the front 



