6 AN INTRODUCTION TO ENTOMOLOGY. 



dorsal aspect of the meso- and metathorax. These become larger 

 and larger with each successive moult, assuming the form of pad- 



FIG. 12. Nymph of Melanoplus, fifth stage. 

 (After Emerton.) 





FIG. -L^.Melanoplus, adult. 



like wing-cases. But these wing-cases never approximate in length 

 the perfect wings of insects in which these organs become fully 

 developed. There is, therefore, usually a very marked change 

 between the last nymph stage and the mature insect. (See Figs. 

 12 and 13.) 



With the nymphs of certain families, dragon-flies, crickets, grass- 

 hoppers, and locusts, the wing-cases are inverted ; i.e., the aspect cor- 

 responding to the upper side of the 'wing is next to the. body, and 

 the first pair of wing-cases extend back beneath the second pair. 

 This characteristic is useful in distinguishing the adult forms from 

 the nymphs of those species in which the wings never become fully 

 developed. 



