150 INVERTEBRATE ANIMALS. 



oviparous. Generally speaking, the young insect is extremely 

 different in external character from the adult, and it requires, 

 before reaching maturity, to pass through a series of changes 

 which collectively constitute what is called the " metamor- 

 phosis. In some insects, however, there is no proper meta- 

 morphosis, and in some the changes which take place are not 

 so complete and striking as in others. By the ^sence of mei^ 

 amorphosis, or by its completeness when present, insects are 

 divided into three convenient, though perhaps not strictly 

 natural, sections, as follows : 



Section I. Ametabolic Insects. — The insects belonging to 

 this section are said to be "Ametabolic" (Gr. a, without; 

 metabole, change), because they pass through no metamorpho- 

 sis. The young, on their escape from the egg, resemble the 

 adult in every respect except in size, and they undergo no 

 alteration in reaching maturity, except that they grow larger. 

 AU the insects of this section are destitute of wings in the 

 adult state, and they are therefore often called " Aptera " 

 (Gr. a, without ; pteron, a wing). 



Section II. Semimetabolic Insects. — In the insects be- 

 longing to this section (Gr. hemi, half; and metabole, change), 

 there is a metamorphosis consisting of three stages, but these 

 stages do not differ much from one another in appearance. 

 The young, on escaping from the egg, is known as the " larva," 

 and it is not only much smaller than the adult, but is desti- 

 tute of wings. After several changes of skin, the larva enters 

 into the second stage, when it is termed the " pupa." The 

 pupa is active and locomotive, and rarely differs much from 

 the larva, except that it is bigger, and rudimentary wings 

 have now appeared on the back of the thorax. After a cer- 

 tain period, and after some changes of skin, the wings burst 

 from their sheaths, and the pupa is now converted into the 

 third and final stage, when it is known as the " imago " or 

 perfect insect. In all the insects belonging to this section — 

 such as grasshoppers, dragon-flies, etc. — the second stage or 

 pupa is active and locomotive ; and for this reason the meta- 

 morphosis is said to be " incomplete.' 



Section III. Hblometabolic Insects (Gr. holos, entire ; and 

 metabole, change). — The insects belonging to this section — 

 such as butterflies, moths, and beetles — ^pass through three 

 stages, just as do the preceding, but these stages differ from 



