40 THE LIFE-STORY OF INSECTS [CH. 



within the body-wall of the larva, is really a double 

 fold of the epidermis, the outer fold forming the 

 pouch, the inner the actual wing-bud. Into the 

 cavity of the latter pass branches from the air-tube 

 system. In its earliest stage, the wing-bud is simply 

 an ingrowing mass of cells (fig. 10 A) which sub- 

 sequently becomes an inpushed pouch (B). Until 

 the last stage of larval life the wing-bud remains 

 hidden in its pouch, and no cuticle is formed over it. 

 When the pupal stage draws near the bud grows out 

 of its sheath, and projecting from the general surface 

 of the epidermis becomes covered with cuticle to 

 be revealed, as we have seen, after the last larval 

 moult, as the pupal wing. Thus all through the life 

 of the humble, crawling caterpillar, t it doth not yet 

 appear what it shall be,' but there are being pre- 

 pared, hidden and unseen, the wondrous organs of 

 flight, which in due time will equip the insect for 

 the glorious aerial existence that awaits it. 



As mentioned above, this hidden growth of the 

 wing-rudiments, in butterflies, beetles, flies, bees, 

 and the great majority of the winged insects, has 

 been emphasised by Sharp (1899) as a character 

 contrasting markedly with the outward and visible 

 growth of the wing-rudiments in such insects as 

 cockroaches, bugs, and dragon-flies. The divergence 

 between the two modes of development is certainly 

 very striking, and a conceivable method of transition 



