10 
INSECTS IN GENERAL. 
Iu those moths which have bi-pectiuate antennae, these parts are 
almost always wider iu the males. Many insects in the order ot Diptera 
are remarkable for the great size and beauty of their eyes, and these 
organs are almost always larger in the males than in the females. 
. q In describing insects it is customary, for the sake of brevity, 
(V" -V to distinguish the sexes by signs, as shown iu the margin. 
inale. female. 
EXTERNAL STRUCTURE OF INSECTS. 
The classification of insects depends chiefly upon the structure of the 
external and visible parts. It is necessary therefore that the student 
should have a thorough knowledge of these parts and of the names 
by which they are designated. But as these parts are very greatly 
modified m the different orders of insects, we shall reserve a minute 
description of them till we come to treat of them in connection with 
the several orders respectively, and shall here give only a general enu- 
meration of them. The student will be much aided in understanding 
the following description by comparing it with the figure of Harpalm 
caliginosus on a subsequent page. 
THE HEAD AND ITS APPENDAGES. 
It often becomes necessary to refer to different parts of an insect’s 
head, and they are therefore designated by particular names indicative 
of their situation. These are — 
The Hind-head, [Occiput). The Crown, (Vertex). The Forehead 
(From). The Face, ( Facies ). The Cheeks, (Gernv). 
The appendages of the head are the Horns, (Antenna;) ; the Eyes, 
(Oculi) ; and the parts of the Mouth, (Trophi, or oral organs.) 
The Antennw. — All insects have two more or less elongated and 
usually mauy-jointed antenna; situated one on each side of the head, 
and varying greatly, iu different kinds ot insects, in length and in the 
form of their component joints. Insects have very short antennae in 
their larva state, and in some perfect insects, such as the water-beetles, 
(Gyrini and Hydrophili), the antennae are not longer than the head, 
whilst in others, such as some of the longicorn beetles, they are more 
than twice as long as the whole body, and in some of the small moths 
of the genus Adela , they are five or six times as long. The uses of the 
antenna; are not known, but, as we have stated above, when treating ot 
the senses of insects, they are supposed to be instrumental in the sense 
of hearing. The most common variations in the forms of the antenna; 
are expressed by the following terms. Figures of most of these forms 
are given on a subsequent page, in treating of the Coleoptera. 
Filiform, or thread-like ; long aud slender, and ot the same, or ueaily 
the same width throughout. 
