1(58 



NATURAL HISTORY OF ARTHROPODS. 



the wings are entirely wanting or in which they are only in a rudimentary condition 

 pass through fewer moults than those possessing full wings. Among many of those 

 forms that have the wings rudimentary it is sometimes quite difficult to distinguish the 

 pupa from the imago. In such cases a safe criterion will be found in the presence or 

 absence of articulation in these appendages. Another and unerring criterion by which 

 the pupa and imago of such species may be distinguished will be found in the position 

 of the wings. The elytra of the pupa are thrown back and twisted around so that the 

 surfaces and margins are precisely reversed when closed as compared with the imago 

 or perfect state. That which is to be the inner surface in the imago is the outer 

 surface in the pupa ; the costal margin which is inferior in the imago is the upper or 

 anterior margin in the pupa ; the apical veins which curve upward in the former curve 

 downward in the latter. This peculiar arrangement, in connection with the others 

 mentioned, will enable anyone to determine whether a short-winged specimen is a pupa 

 or a mature insect. 



The chief characters used in the classification of orthopterous insects are the 

 genitalia, the mouth-parts and the antennre ; though other characters are largely 

 used, as position and form of the eyes, form and comparative length of wings and 

 legs, shape of the head, thorax, and general contour of the whole insect. The cerci 



FIGS. 244 and 245. End of abdomen of male and female locust (Acrydlum}; d, cerci; y h, ovipositor; 



*, egg guide. 



and ovipositor have, however, become recognized within the past few years as the 

 most reliable characters by which species and even genera can be recognized. Especi- 

 ally is this true among the Acrididoe or locusts, where neither size, color, nor the 

 presence or absence of well-developed wings signify specific differences. The sexual 

 organs are most characteristic in the male in some of the families ; those of the female 

 most so in others ; Avhile in still others these organs in both sexes are of equal import- 

 ance for classificatory purposes. 



The mouth-parts of the Orthoptera, although varying somewhat among the 

 different families, are essentially the same. All the representatives of the order have 

 these parts admirably fitted for biting and gnawing the substances upon which they 

 feed. There are three pairs of these appendages. The true jaws or mandibles are 

 single-jointed, broad, short, and solid, with a toothed cutting and grinding edge. Be- 

 hind the mandibles are the maxilla?, which are accessory jaws, and serve to hold and 

 arrange the food to be ground by the true jaws. The floor of the mouth is formed by 

 the labium which in reality is composed of a second pair of maxillae, soldered together 

 in the middle. Both the maxillae and the labium are furnished with a pair of jointed 

 feelers which also aid in the process of feeding. In front of all these hangs the labrum 

 or lip, a loose flap that covers the jaws like a curtain when they are closed. 



