INTRODUCTION 3 



special provisions enabling it to breathe dissolved air. But 

 in its general build its broad head, its six conspicuous legs, 

 its tapering hind-body the aquatic larva of the dragon-fly 

 resembles its parent far more closely than the caterpillar 

 resembles the butterfly. And, in marked contrast to the 

 course of growth in the life of the last-named insect, the young 

 dragon-fly at an early age possesses on the second and third 

 segments of the fore-body visible rudiments of wings, which 

 become larger as the creature passes from stage to stage of 

 its existence. 



Further, if the observer can find specimens as young as 

 possible of the insect first mentioned in this brief survey, 

 a grasshopper, he will see at once that the little creature 

 resembles its parent as unmistakably as a kitten resembles 

 a cat, or a cygnet a swan. The baby grasshopper has the 

 same general shape of body as the adult, the same long, 

 strong hind-legs serviceable for jumping ; it lives in the same 

 situation as its parent and devours the same kind of food. As 

 yet, indeed, it has no trace of wings ; but early in the course 

 of its growth rudiments of these organs appear on the proper 

 body-segments, and they become more prominent at each 

 successive stage. 



Lastly, should our rambler turn over a stone or pull a strip 

 of bark from a dead tree-trunk, he will probably see a number 

 of tiny insects actively leaping about. They are spring-tails, 

 and if they be examined with a lens it will be found that the 

 young closely resemble the adults, which differ from all the 

 fully-grown insects mentioned hitherto, in having no wings. 

 In the case of these spring-tails, therefore, there is even less 

 difference between the young and the adult than in the 

 case of the grasshopper, as in all its stages a spring-tail 

 is wingless. 



These few examples are sufficient to illustrate superficially 

 the varying degrees of change among insects during their 

 growth from the newly-hatched young to the perfectly-formed 

 adult. A wide field of inquiry is thus opened up, and it will 

 be found that a study in some detail of the stages through 

 which these and similar creatures pass will afford facts of 

 surpassing interest and suggest lines for fascinating 

 speculation. Before entering more fully, however, on the 



