270 



ANIMAL STUDIES 



ling one. But we know that development in other animals 

 is a gradual and continuous process, and so it is in the 



case of the butterfly. 

 The gradual chang- 

 ing is masked by the 

 outer covering of the 

 body in both larva 

 and pupa. It is only 

 at each molting or 

 throwing off of this 

 unchanging, unyield- 

 ing chitin armor that 

 we perceive how far 

 this change has gone. 

 The longest time of 

 concealment is that 

 during the pupal or 

 chrysalis stage, and 

 the results of the 

 changing or develop- 

 ment when finally re- 

 vealed by the split- 

 ting of the pupal 

 case are hence the 

 most striking. 



243. Metamorphosis among other animals. Many other 

 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 boot-jack shaped body called the pluteus stage (Fig. 150). 

 In the pluteus a skeleton of lime is formed, and the final 

 true sea-urchin body begins to appear inside the pluteus, 

 developing and growing by using up the body substance of 

 the pluteus. Star-fishes, which are closely related to sea- 



FIG. 149. Larva of a butterfly just changing into 

 pupa (making last larval molt). Photograph 

 from nature. 



