DEVELOPMENT 



28 3 



In the large class of Insecta the development is characterized 

 by more or less complete metamorphosis (see Figs. 115 and 117). 



In the life history of the frog and the salamander we find a 

 metamorphosis that is as well marked in some ways as that of the 

 insects (see Fig. 118). 



A complex animal, developing from a single cell, passes 

 through a number of stages that are different from the 

 finished form, on the one 

 hand, and from the simple 

 beginning, on the other. 

 This is really all that 

 metamorphosis means 

 when applied to living 

 things in general. It is 

 another name for devel- 

 opment. But when we 

 use the latter term, we 

 have in mind the process, 

 whereas when we say 

 " metamorphosis," our 

 attention is fixed on the 

 forms, or stages. 



330. Metamorphosis in 

 man. The changes that 

 take place in a human 

 being from day to day are 

 comparatively slow, and 



the form of the infant is in general very much like that of the 

 adult, so that we do not commonly think of the metamorphosis 

 of human beings. But if we compare the proportions of a 

 baby with the proportions of an adult, we can see that the 

 changes are real even in the outward form (see Fig. 119). 

 A man is something more than a large baby, something 

 different, even in this outward form. We know, of course, 

 that as we become older there are many changes in the internal 



FIG. 119. Metamorphosis in man 



A comparison of the infant and the adult shows 

 that after birth the legs of the baby grow more than 

 any other part, whereas the head grows the least. 

 A study of this figure will show other changes 

 that take place in the outward form 



