i6 



INSECT TRANSFORMATION 



seen, to a great extent protective. With such an arrangement 

 may be contrasted, on the one hand, that found in dragon- 

 flies, where fore- and hindwings are alike flying-planes of great 

 strength and rigidity, and on the other hand, the highly- 

 specialized condition in many beetles, where the forewings 

 are modified into hard, thickened sheaths, the hindwings 

 alone being used for the support of the insect when flying. 



As the changes through which insects pass during their lives 

 are largely concerned with the development of the wings, the 

 form and arrangement of these organs are worthy of attention 

 in some detail. The wing is attached at its base to the segment 

 that bears it, articulating with the exoskeleton of the thorax 

 by means of a group of firm sclerites (Fig. 5, i, 2, 3, 4 P) the 

 outermost of which are continuous with the principal longi- 



FIG. 7. FORE-WING OF MALE GRASSHOPPER 



Co, costa; T, termen ; D, dorsum ; SC, subcostal ; R, radial ; M, median ; C, cubital ; A, anal 

 nervures. x 8. From Comstock, " Introduction to Entomology ". 



tudinal nervures described below. The front edge of the wing, 

 when extended at right angles to the axis of the body is called 

 the costa (Fig. 7 Co), the hinder edge the dorsum and the outer 

 boundary the termen. In the large sub-triangular hindwing 

 of the grasshopper the dorsum and termen are both extensive, 

 but in the narrow forewing with its rounded tip these sections 

 of the margin are hardly distinguishable except as indicated 

 by the nervuration. The longitudinal nervures which traverse 

 the wing from base to termen are of great functional import- 

 ance because they are the chief support of the delicate wing- 

 membrane ; they are also valuable guides to the student of 

 insect classification and development. Running nearly parallel 

 to the costa is the sub-costal nervure, then connected with the 

 same group of basal sclerites, the great radial trunk which 



