THE LIFE CYCLE 97 
developing and growing by using up the body substance of 
the pluteus. Star-fishes, which are closely related to sea- 
urchins; show a simi- 
lar metamorphosis, 
except that there is 
no pluteus stage, the 
true star-fish-shaped 
body forming, with- 
in and at the expense 
of the. first larval 
stage, the ciliated 
free-swimming stage. 
A young crab just 
issued from the egg 
(Fig. 48) is a very 
different appearing 
creature from ‘the 
adult or fully devel- 
oped crab. The body 
of the crab in its 
first larval stage is 
composed of a short, 
globular portion, fur- 
nished with conspicuous long spines and a relatively long, 
jointed tail. This is called the zoéa stage. The zoéa 
changes into a stage called the megalops, which has many 
characteristics of the adult crab condition, but differs espe- 
cially from it in the possession of a long, segmented tail, 
and in having the front half of the body longer than wide. 
The crab in the megalops stage looks very much like a 
tiny lobster or shrimp. The tail soon disappears and the 
body widens, and the final stage is reached. 
In many families of fishes the changes which take place 
in the course of the life cycle are almost as great as in the 
case of the insect or the toad. In the lady-fish (Albula 
vulpes) the very young (Fig. 49) are ribbon-like in form, 
8 
Fie. 48.—Metamorphosis of the crab. a, the zoéa 
stage; b, the megalops; ¢, the adult. 
