FORM, GROWTH, AND CHANGE 17 



gives off the branched radial sector. Close alongside the 

 radial is the median, though this springs in some cases from 

 the hinder group of sclerites, associated in its origin with 

 the cubital and anal nervures, the last-named two or three 

 in number. The area traversed by these anal nervures in the 

 hindwing is that which can be folded fanwise beneath the 

 firmer front region, and in many insects a similar arrange- 

 ment is to be noticed. 



The radial, median and cubital nervures are often branched 

 to a greater extent than in the grasshopper, five radial, three 



FIG. 8. WING-RUDIMENTS OF AN IMMATURE GRASSHOPPER, 

 SHOWING TRACHEAL TRUNKS. 



Sc, sub-costal ; R, radial (Rs, radial sector) ; M, median ; 

 Cu, cubital; ist A, first anal. After Comstock, "Wings of 

 Insects ". 



or four median and two cubital branches being frequently 

 recognizable (Figs. 35, 87). Between the longitudinal nervures 

 fine transverse nervules are often developed in large numbers, 

 and this condition is strongly marked in the grasshopper, whose 

 wing-areas present the appearance of a complex network. 

 The larger nervures contain blood-spaces and are traversed 

 by air-tubes, outgrowths of the remarkable breathing-system 

 of the insect that has yet to be considered. The growth of 

 these air-tubes or tracheal trunks into the cavity of the develop- 

 ing wing indicates the general course of the subsequently 

 formed nervures (Fig. 8). 



2 



