2 INSECT TRANSFORMATION 



where food was plentiful, such as the inside of plant-tissues, 

 the carcase or excrement of some animal, the mud of the pond- 

 shore, the waters of the ditch or stream. The dragon-fly's 

 few weeks of aerial hunting are preceded by a year or two of 

 lurking existence as a crawling " larva " or " nymph " at the 

 bottom of the pond or river. Growth accompanied by change 

 is thus the rule of life in the insect world. 



Somewhat more detailed study shows us that the changes 

 which accompany growth vary greatly in their extent in 

 different groups of insects. Let us start, for example, with 

 the transformation that is more familiar than any other 

 that of the caterpillar into the butterfly. There are many 

 striking features of difference : the caterpillar is wingless, 

 crawling, biting ; the butterfly is winged, flying, sucking. 

 Yet in both there are obvious correspondences, such as the 

 firm head capsule with its feelers, and behind the head the 

 three segments of the fore-body, each segment with its pair 

 of legs. A greater difference than this is noticeable between 

 the wasp or bee and its grub ; though the latter has a head- 

 capsule distantly resembling that of its parent, it has no legs 

 of any kind. And between the blow-fly and its maggot, there 

 is a divergence still greater, for the maggot is not only without 

 legs, but without a recognizable head-region. Thus the life- 

 stories of a butterfly, a bee, and a blow-fly form a series illus- 

 trating increasing divergence between the larva (as all young 

 creatures unlike their parents are commonly called) and the 

 imago (or adult, winged creature). In all these insects there 

 is much change during growth, and the greater the difference 

 between larva and imago, the more profound the change must 

 be. Between the larva and the imago comes, in the course 

 of the life-history, the resting stage which is called the " pupa ' 

 or " chrysalis " ; before and during this period much recon- 

 struction of the body necessarily takes place. It is noteworthy 

 that in butterfly, bee, and blow-fly, no trace of wings can be 

 seen until the pupal condition has been assumed. 



If, however, the life-story of a dragon-fly be compared with 

 that of a butterfly, considerably less distinction between the 

 young and the adult insect is to be noticed. There are indeed 

 striking differences in many details of structure, notably in 

 the jaws, and the immature insect living under water has 



