66 INSECT TRANSFORMATION 



The three insect life-histories, which it has been sought to 

 sketch in sufficient detail for the appreciation of their salient 

 features, illustrate therefore an increasing divergence in form 

 between the adult and the young. In succeeding chapters 

 many further examples of this most important aspect of insect 

 transformations will be given ; it will be seen, for example, 

 that the common flesh-eating maggot differs far more pro- 

 foundly from its parent blue-bottle than the caterpillar differs 

 from the butterfly, though its mode of growth is essentially 

 of the same type. Such insects, whose wing-rudiments, 

 hidden in the larva, appear outwardly only in the resting pupa, 

 are often said to pass through a " complete transformation " 

 and are defined as holometabolous , while the type of life- 

 history exemplified by the dragon-fly has been defined as an 

 " incomplete transformation ", insects conforming to it being 

 distinguished as hemimetabolous ; the grasshopper which, 

 after hatching, undergoes no conspicuous change except the 

 acquisition of wings might be regarded as an ametabolous 

 insect, or one with no feature in the life-history that can 

 fairly be regarded as a " transformation ". Thus each of the 

 three insects might be taken to represent a special section of 

 the class to which they belong when studied from the stand- 

 point of development. But it must be admitted that between 

 the grasshopper and the dragon-fly as between the butterfly 

 and the blue-bottle the developmental difference is one of 

 degree, while between the grasshopper and the dragon-fly on 

 the one hand and the butterfly and blue-bottle on the other, 

 there is a distinction that seems fundamental. The two 

 former have outward and visible wing-rudiments ; in the 

 latter these structures grow so as to be concealed until the 

 characteristic pupal stage is reached. This fundamental 

 distinction has been emphasized in recent years 1 by laying 

 stress on the contrast between the outward and the inward 

 (exopterygote and endopterygote) or as they might perhaps be 

 suitably termed the "open' and the "hidden' types of 

 wing development, further examples of which will be discussed 

 respectively in the next two chapters of this book. 



1 D. Sharp : " Some Points in the Classification of Insects ". Fourth 

 Internal. Zoolog. Congress, 1898. Cambridge, 1899. 



