176 SI-. 



the beetles they are upward of -3,000; iii the silk-worm 

 moth they are 6,236 ; in the dragon-fly 12,544, and in 

 some insects they amount to 20,000. 



538. The appearance of this compound eye in the me- 

 lolontha, yellow beetle, or may-bug, when highly magni- 

 fied, is shown by Fig. 105. 



539. Eye of the Yellow Beetle magnified. It may be 

 observed that the eye of this insect is regularly divided 

 into hexagonal or six-sided sections, Fl<r ]05 

 while the interior of each tube is 



round. The design of giving in- 

 sects such a number of eyes, is evi- 

 dently that they may be enabled to 

 see in all directions without moving 

 the eye-ball or head, as will be 

 shown directly. 



540. Magnified, Eye of a Butterfly. In the phalena, a 

 genus of butterflies, and in some other tribes, the little 

 eyes are arranged into squares instead Fig. 106. 



of hexagons, as shown by Fig. 106. 

 The design of this variety in different 

 species is unknown, but undoubtedly 

 some purpose of convenience to the in- 

 sect is answered by it. 



541. Structure of the Compound Eyes of Insects. 

 Naturalists have investigated with great care and consid- 

 erable labor the structure of the compound eyes of insects. 

 The following account of the mechanism of the eye of the 

 libellula vulgata, or gray dragon-fly, is the result of the 

 observations of M. Duges, a French naturalist. The fig- 

 ures of course are magnified, some of them many hundred 

 times. 



542. The whole outside surface of the compound eye, 

 c c, Fig. 107, may be considered as corresponding to the 

 cornea of animals. Each separate division of this par/ 

 in insects is called corneule, or little cornea. These 

 are shown by the waved line on the circumference of 



