92 ORGANS OF SENSE IN INSECTS. 



causes the formation of the Gall-nuts, of which so much use is 

 made in the manufacture of ink, and in the preparation of black 

 dyes. The small puncture effected by the Cynips causes an 

 overflowing of the vegetable juices, and there soon results from 

 this, an excrescence, in the centre of which we find the eggs, 

 or larvae, of the insect. 



668. Insects are provided with highly developed senses; 

 they evidently possess Hearing and Smell, as well as Taste, 

 Sight, and Touch ; but even now the seat of the sense of 

 Smell has not been certainly discovered ; and amongst the 

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

 be perceived. The antennae, 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 



t, r.^1 IT, /I oro FIG. 410. Head and eyes of the Bee: a, a, antennae; A, facets 



hexagonal, ana ai e en i a rged ; U, the same with hairs growing between them. 



united together, so 



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 



