266 ANIMAL STUDIES 



241. Metamorphosis. While a young robin when it 

 hatches from the egg or a young kitten at hirth resembles its 

 parents, a young star-fish or a young crab or a young butter- 

 fly when hatched does not at all resemble its parents. And 

 while the young robin after hatching becomes a fully grown 

 robin simply by growing larger and undergoing compara- 

 tively slight developmental changes, the young star-fish or 

 young butterfly not only grows larger, but undergoes some 

 very striking developmental changes ; the body changes 

 very much in appearance. Marked changes in the body of 

 an animal during post-embryonic or larval development 

 constitute what is called metamorphic development, or the 

 animal is said to undergo or to show metamorphosis in its 

 development. Metamorphosis is one of the most interest- 

 ing features in the life history or development of animals, 

 and it can be, at least as far as its external aspects are con- 

 cerned, very readily observed and studied. 



242. Metamorphosis among insects. All the butterflies 

 and moths show metamorphosis in their development. So do 

 many other insects, as the ants, bees, and wasps, and all the 

 flies and beetles. On the other hand, many insects do not 

 show metamorphosis, but, like the birds, are hatched from 

 the egg in a condition plainly resembling the parents. A 

 grasshopper (Fig. 146) is a convenient example of an insect 

 without metamorphosis, or rather, as there are, after all, 

 a few easily perceived changes in its post-embryonic devel- 

 opment, of an insect with an "incomplete metamorpho- 

 sis." The eggs of grasshoppers are laid in little packets 

 of several score half an inch below the surface of the 

 ground. When the young grasshopper hatches from the 

 egg it is of course very small, but it is plainly recognizable 

 as a grasshopper. But in one important character it dif- 

 fers from the adult, and that is in its lack of wings. The 

 adult grasshopper has two pairs of wings ; the just hatched 

 young or larval grasshopper has no wings at all. The 

 young grasshopper feeds voraciously and grows rapidly. 



