C INSECTS IN GENERAL. 



Squash-bug fCoreus tristisj, the ocelli are wanting in the larva and i)upa 

 states, but become developed in the last or jierfect stage. 



The compound eyes of insects present one of the most complex and 

 beautiful mechanisms in the organic world. They are two in number, 

 but proportionately very large, occupying in many insects nearly the 

 whole of the sides of the head, and, in the dipterous order especially, 

 often present across their disks, bands of the richest tints of green, 

 brown and purple. These eyes are found to be composed of a great 

 number of lesser eyes or eyelets, in the form of elongated cones so 

 closely compacted as to form apparently a single organ. The larger 

 ends of these coues point outwards, and by their union form the visible 

 eye. Their smaller extremities point inwards, toward the brain, to 

 which they are connected by means of a large optic nerve. When one 

 of these eyes is examined through a strong magnifying glass, it is seen 

 to be composed of a very great number of little facets, sometimes 

 square, but usually six sided,' each one of which represents the outer 

 and larger extremity of one of the component parts. These facets vary 

 greatly in number in the eyes of different kinds of insects. In the ants 

 there are about fifty in each eye ; in the Sphinx moths, about 1,300 ; in 

 the house fly, 4,000 ; in the butterfly, upwards of 17,000 ; and in some of 

 the small beetles of the genus Mordella, it is said that more than 25,000 

 facets have been enumerated in one compound eye ; so that if we sup- 

 pose that each of these comi)onent parts possesses the power of separate 

 vision, one of these insects must have more than 50,000 eyes. How vi- 

 sion is effected, or how a unity of impression can be produced by so 

 comi^lex an organ, we are unable to conceive. 



Hearing. — Insects are evidently affected by loud noises, and moreover, 

 as many insects have the power of jiroducing voluntary sounds, it is 

 reasonable to suppose that they possess the sense of hearing. No or- 

 gan, however, which has been generally admitted to be an organ of 

 hearing, has been discovered. It is the most common opinion of ento- 

 mologists that the antenna? are instrumental in receiving the impres- 

 sions of sound, and that the sense of hearing is located at or near their 

 place of attachment to the head, and this view is much strengthened by 

 the fact that in some of the larger crustaceans, such as the lobster and 

 crab, a distinct organ of hearing is found located at the base of the an- 

 tennae. 



Smelling. — That insects are endowed with the sense of smell, is proved 

 by the fact that the carrion-fly, and other insects which feed upon, or 

 deposit their eggs upon, putrescent matter, detect such substances at a 

 distance, however completely they may be hidden from the sight. The 

 bee also discovers honey under similar circumstances, and it is therefore 

 fair to presume that insects are conducted to flowers, in hidden situa- 



