62 THE TIIOKAX OK iraNK. 



We will next turn to a brief consideration of the 

 second set of locomotive organs of insects, ^.c., th*"- irings. 



WINGS OF GRASSHOPPER (aCRIDA VIRIDISSIMa). 



These organs are wholly different in their structure 

 and derivation from the wings of birds, but merely re- 

 semble them in appearance and functions; hence we say 

 that the wings of insects and birds are 7iot homologous^ 

 but are merely analogous. The wings of insects, however, 

 are derived from organs termed spiracles, Avith which 

 the insect breathes, although they widely diifer from 

 them in functions and appearance ; hence, also, we may 

 say that the wings of insects are homologous with their 

 spiracles, though not analogous with them. 



We may observe the wings of insects in relation to 

 their number^ kinds^ and composition. 



I Number. — Most insects liave four wings, but in al- 

 most every order, instances occur of insects that have 

 solely a single pair, or even none at all. The latter 

 kind, (those witliout wings), were formerly ranked in a 

 distinct sub-order by themselves, termed " aptera^'' but 

 this is merely an artificial sub-order, and its members be- 

 long to the several natural sub-orders we shall hereafter 

 mention. 



II Kindi. — Under this head we may consider the wings 

 of insects in relation to their situation nnd their 

 substance. 



