i62 THE BIOLOGY OF INSECTS 



In the simple direct type of insect- growth, where the 

 young, after hatching, resembles the adult in all essential 

 features, as in grasshoppers, cockroaches, and bugs (Fig. 4), 

 for example, the only marked changes observable in the 

 successive stages are those due to the development of the 

 wings and, in some insects, to the appearance of the female's 

 ovipositor and other processes or appendages connected 

 with reproduction. An insect's wings arise as hollow paired 

 outgrowths of the second and third thoracic segments, their 

 cavities are continuous with the great blood-space of the 

 body and sets of air-tubes grow into them. After the first 

 or second moult in the life-history of a young cockroach or 

 grasshopper the wing-rudiments can be seen as rounded 

 lobes projecting at the hinder corners of the mesonotum 

 and metanotum, and after each successive moult they become 

 larger than before, displaying in some cases, on the surface 

 of the cuticle, branching tracks which indicate the courses 

 of the air-tubes within. The wing-rudiments, which may 

 be regarded as flattened pouches, become more markedly 

 flattened as their areas extend so that they approximate to 

 the condition in the adult insect. But even in the stage 

 before the final moult, the wing rudiments of an immature 

 cockroach, grasshopper, or bug are shorter by far than the 

 wings of the adult insect. It is necessary, therefore, as part 

 of the preparation for this moult, that the wings should grow 

 extensively and rapidly beneath the separated cuticle and 

 thus something of a crisis is apparent at this stage of develop- 

 ment. When the last moult has taken place the newly 

 exposed wings are seen to be greatly folded or crumpled, 

 a necessary condition of their extensive growth beneath the 

 cuticle of the penultimate instar. When exposed they 

 unfold and flatten from the base outwards, the cuticle 

 becomes hard and firm, and the floor and roof of the hollow 

 outgrowth of the body from which the wing arises become 

 approximated together except along the courses of the air- 

 tubes where the thickened cuticle forms the supporting 

 tubular nervures or " veins " of the wing. 



In such life-histories as those that have been briefly 



