CHAPTER IV 



THE DEVELOPMENT OF INSECTS 



Most insects lay eggs which hatch after a longer or shorter time into 

 the young. In some cases the egg appears to be retained within the 

 body of the parent until after it has hatched, and then the young are 

 produced in a stage able to move about. Insects in which this is true 

 are termed viviparous, the others being oviparous. 



Insect eggs are usually very small; vary greatly in form, and may be 

 laid singly or in clusters (Fig. 31). They are covered by a chitinous 

 shell, the chorion, which often bears markings in the form of ridges, 



B 



FIG. 31. Eggs of various insects. A, butterfly; B, house fly; C, chaleid (Brucho- 

 phagus); D, butterfly; E, midge; F, bug (Triphleps) ; G, bug (Podisus); H, Pomace fly. 

 All much enlarged. (From Folsom.) 



reticulations, etc., and frequently they are also colored. At one place on 

 the surface is a minute opening or group of openings through the shell, 

 called the micropyle, believed to be for the entrance of the fertilizing 

 sperm. The length of time spent in the egg differs in different insects 

 from a few hours to many months, and in some cases the eggs do not 

 hatch until the second season after they are laid. 



In hatching, the shell breaks and out of it crawls the young insect, in 

 the majority of cases quite unlike the adult it is to become. In order to 

 reach maturity it must now grow, and undergo changes in structure and 

 appearance. These together are expressed by saying that most insects 

 in order to become adult undergo a metamorphosis. In some of the 

 simpler insects, a few changes and growth only, are needed to make them 

 mature, and these are therefore usually grouped together as the Ameta- 

 bola, or insects having practically no metamorphosis. 



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