118 T1IK Ul-'K STORY OF INSIST- [CH. 



of the higher insects almost certainly corresponds 

 with the may-fly's sub-imago, and the facts just re- 

 called as to remnants of pupal activity suggest that 

 in the ancestors of endopterygote insects what is 

 now the pupal instar was represented by an active 

 nymphal or sub-imaginal stage, possibly indeed by 

 more than one stage, as Packard and other writers 

 have stated that pupae of bees and wasps undergo 

 two or three moults before the final exposure of the 

 imago. Such an early pupal instar has been defined 

 as a 'pro-nymph' or a 'semi-pupa.' Examples have 

 been given of the exceptional passive condition of 

 the penultimate instar in Exopterygota. The instars 

 preceding this presumably had originally outward 

 wing-rudiments in all insect life-histories, and the 

 endopterygote condition was attained by the post- 

 ponement of the outward appearance of these to 

 successively later stages. The leg and wing rudi- 

 ments of the male coccid (pp. 20-1) beneath the cuticle 

 of the second instar are strictly comparable to 

 imaginal buds, and these are present in one instar 

 of what is generally regarded as an exopterygote 

 life-history. The first instar in all insects has no 

 visible wing-rudiments, but when they grow out- 

 wardly from the body, they necessarily become 

 covered with cuticle, so that they must be visible 

 after the first moult. There is no supreme difficulty 

 in supposing that the important change was for these 



