96 ANIMAL LIFE 
we know, on insects and snails and worms. The metamor- 
phosis of the toad is not so striking as that of the butter- 
fly, but if the tadpole were inclosed in an unchanging 
opaque body wall while it was losing its tail and getting its 
legs, and this wall were to be shed after these changes were 
made, would not the metamorphosis be nearly as extraordi- 
Fie. 47.—Metamorphosis of sea- 
urchin. Upper figure the adult, 
lower figure the pluteus larva. 
nary as in the case of 
the butterfly? But in 
the metamorphosis of 
the toad we can see the 
gradual and continuous 
character of the change. 
59. Metamorphosis among other animals——Many othe1 
animals, besides insects and frogs and toads, undergo meta. 
morphosis. The just-hatched sea-urchin does not resemble 
a fully developed sea-urchin at all. It is a minute worm- 
like creature, provided with cilia or vibratile hairs, by means 
of which it swims freely about. It changes next into a curi- 
ous bootjack-shaped body called the pluteus stage (Fig. 47). 
In the pluteus a skeleton of lime is formed, and the final 
true sea-urchin body begins to appear inside the pluteus, 
