172 THE INSECT WOBLD. 



support the two membranes mentioned above, and which branch 

 out from the base to the edge of the wing. Their number, count- 

 ing from the exterior edge, is not always the same in the upper 

 and lower wings. It varies from eight to twelve. 



With its large and light wings, the butterfly can fly for a long 

 time. But this flight is not in the least regular, it is not made 

 in a straight line. When the insect has to go some distance, it 

 flies alternately up and down. The line it takes is composed of 

 an infinity of zig-zags, going up and down, and from right to left. 

 This irregularity of its flight saves the little insect from falling a 

 prey to birds. " I saw one day with pleasure," says Reaumur, 

 " a sparrow which pursued in the air a butterfly for nearly ten 

 minutes without being able to catch it. The flight of the bird 

 was nevertheless considerably more rapid than that of the butter- 

 fly, but the butterfly was always higher or lower than the place 

 to which the bird flew, and where it thought it would catch it." 



But let us leave the wings to pass on to the other parts of the 

 butterfly. These other parts are the thorax or chest, the body or 

 abdomen, and the head. 



The thorax is solidly put together so as to bear the move- 

 ments of the wings and legs. These latter are composed, as in 

 other insects, of five parts : the hip, the trochanter, the thigh, 

 the leg, and the tarsus. 



Many butterflies have all their six legs of equal length. In 

 others, the two fore legs are very small, and are not suited for 



Fig. 135. Leg of Butterfly armed with hooks. Fig. 136. Leg not suitable for walking. 



walking. In others, again, they are as it were abortions, deprived 

 of hooks, very hairy, and fixed on to the front edge of the thorax 

 like a tippet. 



This difference of structure may be seen in Figs. 135 and 

 136, one of which represents, after Reaumur, a leg unsuited 

 for walking, very hairy, and terminated in a sort of brush 



