350 LECTURE XVI. 



corium. The primitive cellular basis of the chitine is usually de- 

 monstrable in the thin integument of larvae, and of the smaller 

 parasitic insects, when it presents under the microscope a hexagonal 

 structure * : sometimes the cells show nuclei, as in the larva of Hy- 

 drous piceus. \ In some insects the hairs are beset with smaller 

 hairs ; such barbed hairs, in the processionary moths e. g., are easily 

 rubbed off, and, if they penetrate the skin, occasion intolerable 

 itching. 



With regard to the jointed and aliform appendages of the skeleton, 

 the first pair inserted into the front or upper part of the head, are the 

 antennse, which present a vast variety of shapes and sizes in different 

 Insects, but seem in all to have most intimate relation to the senses of 

 touch and hearing. Their precise function has not, however, yet been 

 well defined. The entomologist avails himself of their various con- 

 formation to obtain charactei'S for the distinction of families, of ge- 

 nera, or of species of Insects ; and a considerable section of the gloss- 

 ology of this extensive department of Natural History is devoted 

 to the technical terms required to express the antennal characters. 

 To the head likewise belong more or less complicated oral instru- 

 ments, called " trophi," or "instrumenta cibaria," modified in some 

 insects to serve for suction, in others, for mastication : they properly 

 fall under the demonstration of the digestive system. 



The jointed legs attached, as before stated, to the three thoracic seg- 

 ments, consist each of a hip, a thigh (Jig.\i.\,K), a leg (Z), and a foot 

 (m), commonly called the tarsus ; but which are not to be taken as 

 answerable to the parts so termed in Human Anatomy. The hip, for 

 example, consists of two joints, called " coxa " and " trochanter," usu- 

 ally the shortest of the whole leg : the foot or "tarsus" includes from 

 two to five joints, and is usually terminated by a pair of diverging 

 hooks or claws : a third hook is found in the chaiFer {Jig- \^2,g) and 

 stagbeetle : the legs of the larvae of the darkling beetles {Meloidce) have 

 three lanceolate hooks. The peculiar powers of moving upon land 

 or in water depend upon the modifications of the forms or proportions 

 of these extremities. In water Insects the tarsi are usually flattened, 

 fringed with hair, and stretched out in the same plane Avith the trunk, 

 like oars. In leaping Insects, the hinder limbs present as dispropor- 

 tionate a development as the legs of the kangaroo. In burrowing 

 Insects, the anterior limbs are distinguished by short, broad, and 

 massive proportions, with a strong and flattened hand like that of 

 the mole, as in this best of Insect burrowers %, which has been called 

 the mole- cricket. Most Insects are able to crawl up vertical walls, 



* XXIV. p. t CCXXXI p. 387. X Piep. No. 4G3, A. 



