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 
Fig. 2.—A Compound cornea (Fig. 2), each facette being a 
ec cornea; but the facettes unite and form 
a common cornea, which is represented by the entire figure: these 
facettes vary in 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 Lrbellula (dragon-fly) . . . B19 6 0 HAG b 
In the genus Papilio (a genus of butterflies) ater ened OO mame 
In Sphing convolvuli (the convolvulus hawk-moth) . . 1,300 ,, 
In Bombyx mori (the common silkworm moth) . . . 6,286  ,, 
Toa qdals) INOWRESI: At al Bo 60) Om eo. 8 og 6 EDOO) 5 
Tras the an taivenyesi nice Ui siiscetn cena ied pea naire iteate rem iiS 50° 55 
iin’ thelcockehiaterk sw (yy vueiiey lane) vcis velailcg ime yy esters O62 Ones 
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 may be considered an 
agglomeration of simple eyes; but internally its structure is 
altogether different. 
On the under side of each facette we find a body of a gelatinous 
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 
in 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 
