places, and they become joined in other places. In this way the three orig- 

 inal layers — outer, inner and middle — give rise to the several kinds of tissues 

 that make up the organs of the animal. 



When a locust or a cockroach comes out of an egg, it is very much like 

 the parent, except that it is very small and lacks wings (see illustration, 

 p. 352). By a series of moltings the animal not only becomes larger but puts 

 on wings and other organs. When the tgg of a moth or of a butterfly 



23 hours 



30 hours 



^^ 



72 hours 



96 hours 



kill Supply House, Inc. 



FOUR STAGES IN THE DEVELOPMENT OF CHICKS 



While Aristotle followed the scientific method to answer the question of how an egg 

 becomes a chick, it was impossible until comparatively modern times to see in great 

 detail just what happens during the development 



350 



