ORGANS OF SENSE IN INSECTS. 



of Smell has not been certainly discovered ; and amongst the 

 greater part of these animals, no special organ of Hearing can 

 be perceived. The antennas, and the appendages of the mouth, 

 seem to be the principal instruments for Touch ; and the former 

 may, perhaps, also serve for the perception of Sound. We also 

 know very little of the apparatus for Taste ; but the organs of 

 Sight have been better studied. The structure of the Eyes is 

 very different from that which we have seen amongst the higher 

 animals. In general, the organ which at first sight appears to 

 be a single eye, is, in reality, formed by the aggregation of a 

 multitude of small eyes, each having a cornea, a vitreous body 

 of a conical form, a layer of colouring matter, and a separate 

 nervous filament. In the common House-Fly, for example, we can 

 reckon four thou- 

 sand of these dis- 

 tinct eyes; and some 

 insects are known, 

 which have more 

 than twenty- five 

 thousand. All these 

 little corneas are 



hexagonal, and are FIG. 310.-Head and eyes of the Bee : a, a, antenna ; A, facets 

 United together SO enl arged ; B > the 8sanc with hairs growing between them. 



as to form a kind of common cornea, whose surface presents a 

 number of divisions, resembling the meshes of a net, visible 

 only by the aid of a magnifying glass. (See ANIM. PHYSIOL. 

 573, 574). Moreover, each of the small eyes, which 

 altogether make up these compound organs, is perfectly distinct 

 from those which surround it, and forms with them a bundle of 

 tubes, each terminated by a nervous thread proceeding from a 

 bulbous expansion of the same Optic Nerve. Nearly all Insects 

 are furnished with two of these compound eyes, usually placed 

 on the sides of the head ; but sometimes they are replaced by 

 simple eyes ; and in other instances these two sorts of organs 

 exist together. The structure of simple eyes, which are known 

 also by the name of stemmata or ocelli, has the greatest analogy 

 with that of each of the elements of the compound eyes. The 

 simple eyes are generally united in a group, to the number of 



