30 ROMANCE OF THE INSECT WORLD CHAP. 



their lightness or over-activity. The muscular efforts 

 of prolonged flight also heighten the animal tem- 

 perature, and this tends to rarefy the air contained 

 in the vesicles and tracheae. 



The question still naturally presents itself: Why 

 do insects undergo metamorphoses ? Why should 

 they, in attaining to maturity, pass through such 

 remarkable development ? and Why should the 

 course of development be apparently separated into 

 three or four distinct states, by marked alteration in 

 form ? 



In the first place it must be observed that most 

 of the animal creation, of the higher classes at any 

 rate, have equally to submit to metamorphoses, or 

 in other words to difference in shape and appear- 

 ance, and also in structure of internal organs, in 

 their early life and in maturity. Thus many animals 

 which when mature differ widely, show points of 

 resemblance to one another in their young state. 

 Besides, the embryo of every organism is believed 

 to portray, more or less completely, the form and 

 structure of its less modified progenitors, so that the 

 changes of a single individual as it were exhibit in 

 miniature, and in short space of time, organic evo- 

 lution in general, which ages of indefinite duration 

 have been requisite to bring about. In fact the 

 great majority of animals do undergo well-marked 

 metamorphoses, but often those most pronounced 

 are passed through within the egg, previous to birth, 

 and thus are not revealed, except to the eyes of 

 the curious. 1 



Birth, it must be remembered, is not the beginning 

 1 Sir John Lubbock. Herbert Spencer. 



