()54 INSECTS : STRUCTURE OF INTEGUMENT. 



inhabitant of our ponds and streams. This Insect passes two 

 or even three years in its Larva state, and during this time it 

 repeatedly throws-off its skin ; the cast Skin, when perfect, is an 

 object of extreme beauty, since, as it formed a complete sheath to 

 the various appendages of the body and tail, it continues to exhibit 

 their outlines with the utmost delicacy; and by keeping these 

 Larvae in a Vivarium, and by mounting the entire series of their 

 cast Skins, a record is preserved of the successive changes they 

 undergo. Much care is necessary, however, to extend them upon 

 slides, in consequence of their extreme fragility ; and the best plan 

 is to place the slip of Glass under the skin whilst it is floating on 

 water, and to lift the object out upon the slide. — A method of 

 cutting sections of Insects, Caterpillars, &c, with the Section- 

 instrument (§ 137), has lately been practised by Dr. Halifax, with 

 most excellent results. The body of the Insect is first soaked for 

 some time in thick Grum-mucilage, which passes into its substance, 

 and gives support to its tissues. It is then enclosed in a casing of 

 Wax, and this again is surrounded by a hollow cylinder of Wood 

 made to fit the cavity of the Section-instrument, which for this 

 purpose must be larger than usual ; and this being raised by suc- 

 cessive turns of the Screw, very thin sections can be obtained, by 

 which the internal parts of the Insect are brought into view in 

 their normal relations. 



511. Structure of the Integument. — In treating of those separate 

 parts of the organization of Insects which furnish the most inte- 

 resting objects of Microscopic study, we may most appropriately 

 commence with their Integument and its Appendages (Scales, 

 Hairs, &c). The body and members are closely invested by a 

 hardened Skin, which acts as their Skeleton, and affords points of 

 attachment to the Muscles by which their several parts are moved ; 

 being soft and flexible, however, at the joints. This Skin is usually 

 more or less Horny in its texture, and is consolidated by the 

 Animal substance termed Chitine, as well as, in some cases, by a 

 small quantity of Mineral matter. It is in the Coleoptera that it 

 attains its greatest development ; the Dermo-skeleton of many 

 Beetles being so firm as not only to confer upon them an extraordi- 

 nary power of passive resistance, but also to enable them to put 

 forth enormous force by the action of the powerful Muscles which 

 are attached to it. It may be stated as a general rule, that the 

 outer layer of this Dermo-skeleton is always Cellular, taking the 

 place of an Epidermis; and that the Cells are straight-sided and 

 closely fitted-together, so as to be polygonal (usually hexagonal) in 

 form. Of this we have a very good example in the superficial 

 layers (Fig- 341, b) of the thin horny lamellae or blades, which 

 constitute the terminal portion of the Antenna of the Cockchafer 

 (Fig. 340) ; this layer being easily distinguished from the inter- 

 mediate portion of the lamina (a), by careful focussing. In many 

 Beetles, the Hexagonal areolation of the surface is often distin- 



