114 THE LIFE-STORY OF INSECTS [CH. 



chapter of this book, widely different though cater- 

 pillar and butterfly may appear at a superficial glance. 

 And the survey of variety in form, food, and habit of 

 insect larvae given iji Chapter vi enforces surely the 

 conclusion that the larva is eminently plastic, adapt- 

 able, capable of changing so as to suit the most 

 diverse surroundings. In a most suggestive recent 

 discussion on the transformation of insects P. Dee- 

 gener (1909) has claimed that the larva must be 

 regarded as the more modified stage, because while 

 all the adult's structures are represented in the larva, 

 even if only as imaginal buds, there are commonly 

 present in the larva special adaptive organs not found 

 in the imago, for example the pro-legs of caterpillars 

 or the skin-gills of midge-grubs. The correspond- 

 ence of parts in butterfly and caterpillar just re- 

 ferred to, may still be traced, though less easily, in 

 bluebottle and maggot. The latter is an extreme 

 example of degenerative evolution, and its contrast 

 with the elaborately organised two-winged fly marks 

 the greatest divergence observable between the larva 

 and imago. With this divergence the resting pupal 

 stage, during which more or less dissolution and re- 

 construction of organs goes on, becomes a necessity, 

 and it has already been pointed out how the amount of 

 this reconstruction is greatest where the divergence 

 between the larval and perfect stages is most marked. 

 Whatever differences of opinion may prevail on points 



