172 THE INSECT WORLD. 
the two membranes mentioned above, and which branch out from 
the base to the edge of the wing. Their number, counting 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 flight saves the little insect from falling a 
prey to birds. “I saw one day with pleasure,” says Réaumur, 
“‘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 butterfly, 
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 movements 
of the wings and legs. These latter are composed, as in other 
insects, of five parts: the coxa, the trochanter, the thigh, the 
shank, 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.—Lee of Butterfly armed with hooks. Fig. 156.—Leg not suitable for walking. 
walking. In others, again, they are as it were abortions, deprived 
of hooks, very hairy, and applied on to the front edge of the breast 
like a tippet. . 
This difference of structure may be seen in Figs. 1385 and 
136, one of which represents, after Réaumur, a leg unsuited 
for walking, very hairy, and terminated in a sort of brush 
