INTRODUCTION - . 
antennae of many beetles, which consist of thin 
chitinous lamellae, may be hygrometric, indicating the 
■state of the atmosphere to the insect. I have little 
doubt, however, in other insects, as in the fly, especially 
when they are thick and club shaped, that the}^ are 
olfactory or rather partly olfactory organs. 5 ’* Some 
years ago I examined a great number of w T asps, with a 
view to satisfy myself on this point; I used the bleaching 
process recommended by Dr. Hicks, but was unable to 
come to any conclusion on this interesting but puzzling 
point. 
Conspicuous on the head of every insect are its two 
large compound eyes of various colours—emerald, blue, 
chesnut, orange, or as beads of burnished gold ; besides 
these are generally to be seen two or three simple eyes, 
oalled ocelli, which are placed on the top of the head 
between the two large compound eyes—these require 
the aid of a lens to render them 
visible. The compound eyes are 
made up of an immense number 
of hexagonal or six-sided facets, 
which in some insects, as in the 
dragon-flies, can be distinguished 
by the naked eye ; each facet is 0oMPOUND Eye of an Ixsect 
in itself a perfect eye, having a cornea, a lens, a pig¬ 
ment-coating, and a nervous filament; the eyes are 
immovable, and as the head is limited as to motion, it 
might be supposed that an insect was not particularly 
sharp sighted, but everyone who has tried to get at the 
blind side of a common house fly, knows how quickly 
* The Anatomy of the Blow-fly, p. 32. 
