130 



FIELD ZOOLOGY. 



larger tribe of insects. Differentiation of cells, tissues, 

 or organs is held by the scientist to mark an upward 

 step in the continuous stream of life. The conspicuous 

 similarity of the wings of these jugate moths thus indi- 

 cates their low position among the Lepidoptera; this is 

 all the more apparent when one becomes familiar with 

 the immense number of differentiations along just this line, 

 which are found in the other great division of the order 



FIG. 57 A. FIG. 57 B. 



FIG. 57, A. Hind wing of a frenate lepidopter, showing the frenulum. 

 FIG. 57, B. Hind wing of a frenate lepidopter, showing wing angle, serving 

 as the frenulum substitute. 



the Frenatse, and not only among the lepidopter s but 

 among the other orders of insects. (Fig. 57, A and B.) 

 Among the beetles, the grasshoppers, and the crickets, as 

 well as the bugs, the wings are so far differentiated as to 

 make the hind wings bear the burden of flight, while the 

 front wings are reduced to wing-covers or elytra as they are 

 called. But in the bees and the wasps the front wings are 

 the main flight pair. In the dragon flies the two pairs of 

 wings share equally in the act of flying, besides acting 

 independently. In the flies the hind pair of wings are 

 represented only by stumps of wings, remains of what in 

 an earlier age in the earth's history may have been an 

 effective pair of wings performing their full share of the 



