CHAPTER 111 



THE OPEN TYPE OF WING-GROWTH 



THE type of development seen in such life-histories 

 as those of the grasshopper and the dragon-fly is 

 characteristic of a large assemblage of insects which, 

 differing widely among themselves in structure and habits, 

 are distributed by systematic students into various orders. 

 In the selection of illustrative facts which it is proposed now 

 to give, some attempt will be made to set forth those modifi- 

 cations of the open type of wing-growth which seem most 

 important for the understanding of insect transformation in 

 its broad aspect. Many details, interesting in themselves, will 

 find therefore no mention in this chapter. 



Some account of the general build of an insect-wing has 

 already been given in connexion with the brief survey of the 

 structure of the adult grasshopper. It may be well now to 

 return to this subject at the outset of our discussion on wing- 

 growth, tracing the main steps in the development of the 

 organ from the early wing-rudiment. 1 This begins as a hollow 

 outgrowth from the junction of the dorsal and pleural regions 

 of its thoracic segment, the columnar cells of the skin 

 (epidermis) forming a sheet which encloses a prolongation 

 of the great body blood-space of the young insect. The early 

 wing-rudiment may be at first tubular in form, but it tends 

 to become flattened through the approximation of its dorsal 

 and ventral walls, the individual cells of the skin becoming 

 spindle-shaped. Into this hollow rudiment grow air-tubes 

 arising from the dorsal trunk of the larva ; in a typical wing- 

 rudiment these tubes correspond with the main nervures of 

 the developed wing already mentioned : costal, subcostal, 

 radial, median, cubital and several anal (Fig. 35) some of 



1 J. H. Comstock : " The Wings of Insects ". Ithaca, New York, 1918. 



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