10 INSECTS IN GENERAI.. 



lu tliose moths which have bi-pectinate antennoe, these parts are 



almost always wider in the males. Many insects in the order of 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 to distinguish the sexes by signs, as shown in the margin. 



male, female. 



EXTERNAL STEUCTURE OF INSECTS. 



The classification of insects depends chieiiy 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 

 modilied in 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 Sarpalus 

 caliginosus on a subsequent page. 



THE HEAD AND ITS APPENDAGES. 



It often becomes necessary to refer to diflerent 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 

 (Frons). The Face, {Fades). The Cheeks, ((rewft'). 



The appendages of the head are the Horns, {Antennw) ; the Eyes, 

 {Oculi) ; and the parts of the Mouth, {Trophi, or 07'al organs.) 



The Antennw. — All insects have two more or less elongated and 

 usually many-jointed antennie situated one on each side of the head, 

 and varying greatly, in different kinds of insects, in length and in the 

 form of their component joints. Insects have very short antenna? in 

 their larva state, and in some perfect insects, such as the water- beetles, 

 {Gyrini and Rydrophili), the antennae are not longer than the head, 

 whdst in others, such as some of the longicorn beetles, they are more 

 tlian 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 

 antenme are not known, but, as we have stated above, when treating of 

 the senses of insects, they are supposed to be instrumental in the sense 

 of hearing. The most common variations in the forms of the antennae 

 are expressed by the following terms. Figures of mo)«t of these forms 

 are given on a subsequent page, in treating of the Coleoptera. 



Filiform, or thread -Ule; long and slender, and of the same, or nearly 

 the same width throughout. 



