
2 THE INSECT WORLD. 
having to encounter hard substances, must be strongly supported. 
The exception to this rule is among insects which live by suction. 
It would be out of place here to mention the numerous modifi- 
cations of the head which are presented in the immense series of 
the class of insects. 
The eyes of insects are of two kinds, called compound eyes, or 
eyes composed of many lenses, united by 
their margins and forming hexagonal 
facettes; and simple eyes, or ocelli, called 
also stemmata. 
The exterior of the eye is called the 

cornea (Fig. 2), each facette being a 
Fig. 2.—A Compound 
ae cornea; but the facettes unite and form 
a common cornea, which is represented by the entire figure: these 
facettes vary 10 size even in the same eye. 
In order to show the immense number of these facettes possessed 
by many insects, we give the following list :— 
In the genus Mordella (a genus of beetles) the eye has 25,008 facettes. 
In the Lebellula (dragon-fly) - + + + ° 12,544 = ,, 
In the genus Papilio (a genus of butterflies) . - - 17,355 5, 
In Sphinx convol pult (the convolvulus hawkmoth) . .- 1,300 —,, 
In Bombyx mori (the common silkworm moth). - -: 6,236. 55 
Tahoe bonsgesfiy 2 Fuss) & Fon wee 4,000 __—,, 
Tn the ant Me t+ otis, oo ee ate eee BO Ri ss 
Tithe cockehater) oi. 2 a eye eee 8,820 4, 
The facettes appear to be most numerous in insects of the genus 
Scarabeus (a genus of beetles). They are so minute, that they can 
scarcely be detected with a glass. 
Looked at in front, a compound eye might be considered an 
agelomeration of simple eyes ; but internally its structure is 
altogether different. 
On the under side of each facette we find a body of a gellatinous 
appearance, transparent, and usually conical ; the base of which 
occupies the centre of the facette in such a manner as to leave 
around it a ring to receive the pigment. This body diminishes 
sn thickness towards its other extremity, and terminates in a point 
where it joins a nervous filament, proceeding from the optic 
nerve. These cones, agreeing in number with the facettes, play 
