3(5 THE LIFE-STORY OF INSECTS [CH. 



Wherein lies the fundamental difference between 

 these Holometabola on the one hand and the Hemi- 

 metabola and Ametabola on the other? It is not that 

 the larva differs from the imago or that there is a 

 passive stage in the life-history ; these conditions are 

 observable among insects with a 'partial' trans- 

 formation as we have seen, though the resting instar 

 that simulates the butterfly pupa is certainly ex- 

 ceptional. It has been pointed out by Sharp (1899) 

 that the most important indication of the difference 

 between the two modes of development is furnished 

 by the position of the wing-rudiments. In all Ame- 

 tabola and Hemimetabola these are visible externally 

 long before the penultimate instar has been reached ; 

 in the Holometabola they are not seen until the 

 pupal stage. 



Attention has already been drawn to the contrast 

 in outward form between a butterfly and its cater- 

 pillar. As in the case of dragon-fly or may-fly, the 

 larval period is essentially a time for feeding and 

 growth, and during this period the larval cuticle is 

 cast four or five, in some species even seven or eight 

 times. After each moult some changes in detail may 

 be observable, for example in the proportions of the 

 body-segments or their outgrowths, in the colour 

 or the closeness of the hairy or spiny armature. 

 But in all main features the caterpillar retains 

 throughout its life the characteristic form in which 



