122 The Life-History of Insects 



concentration. Many of the organs of the imago in 

 such insects, however, do not arise directly by growth 

 from those of the larva and pupa, but are new 

 structures, developed within the larva from rudiment- 

 groups of cells which are known as " imaginal buds" 

 (fig. 80). From the inner skin of a caterpillar, for 

 example, are produced the buds which 

 will develop into the wings and legs of 

 the Butterfly. The head of a Midge or a 

 Fly, with the eyes, feelers, and jaws are 

 developed in an inpushing of the skin 

 reaching back into the thorax of the larva 

 (fig. 81). The food-canal, glands, and 

 air-tubes of a Moth or a Bee spring from 

 imaginal buds. Just before and during 

 the pupal stage the organs, as they existed 

 in the larva, become dissolved, their com- 

 ponent cells breaking down and being 

 absorbed by the blood corpuscles. This 

 degenerative process is known as histolysis. 

 Meanwhile from the imaginal buds the 

 organs of the perfect insect are built up, 

 the energy required being drawn from 

 the stored-up food-material in the blood 

 and fat-body (2, 4, 57 c, 73, 74)- 



Emergence of the Imago. — When 



the adult organs are fully developed, the 



pupa-skin separates from the underlying 



^. leg; 5. wing, tissues as the successive larval skins have 



Highly magni- ,1. . , , . 



fied. c. cuticle; doue, and splits open in the thoracic 



h. hypodermis. . , ■ , r \ • 



After Lowne, regiou to allow the escape of the imago. 



"Blowfly." -^YiQ emergence must be regarded as the 

 last of the series of moults undergone by the insect 

 in the course of its growth. The skin of the new- 

 born imago, when it first comes out of the pupa- 

 skin, is soft, but it quickly hardens on exposure to 



Fig. 80. — Dia- 

 grammatic sec- 

 tions of Imag- 

 inal buds (d.d.). 



