CHAPTER IV. 

 THE METAMORPHOSIS OF INSECTS 



MANY insects in the course of their lives undergo remarkable 

 changes in form ; a butterfly was once a caterpillar, a bee lived first the 

 life of a clumsy footless grub, and flies, which are so graceful and active, 

 are developed from maggots. 



In the following chapters considerable attention is given to 

 descriptions of the changes through which various insects pass; the 

 object of this chapter is merely to discuss the more general features of 

 the metamorphosis of insects, and to define the terms commonly used 

 in descriptions of insect transformations. 



I. THE EXTERNAL CHARACTERISTICS OF THE META- 

 MORPHOSIS OF INSECTS 



The more obvious characteristics of the metamorphosis of insects 

 are those changes in the external form of the body that occur during 

 postembryonic development. In some cases there appears to be but 

 little in common between the successive forms presented by the same 

 insect, as the caterpillar, chrysalis, and adult stages of a butterfly. 

 On the other hand, in certain insects, the change in the form of the 

 body during the postembryonic life is comparatively little. Based 

 on these differences, several distinct types of metamorphosis have 

 been recognized; and in those cases where the insect in its successive 

 stages assumes different forms, distinctive terms are applied to the 

 different stages. 



a. THE EGG 



Strictly speaking, all insects are developed from eggs, which are 

 formed from the primordial germ-cells in the ovary of the female. 

 As a rule, each egg is surrounded by a shell, formed by the follicular 

 epithelium of the ovarian tube in which the egg is developed; and 

 this egg, enclosed in its shell, is deposited by the female insect, usually 

 on or near the food upon which the young insect is to feed. In some 

 cases, however, the egg is retained by the female until it is hatched; 

 thus flesh-flies frequently deposit active larvae upon meat, especially 

 when they have had difficulty in finding it ; and there are other vivi- 

 parous insects, which are discussed later. In this place is discussed 



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