MODE OF VIEWING SURFACES OF INSECTS. 559 



one end and coming to a point at the other, so that the impres- 

 sion conveyed is that of a set of spines projecting obliquely from 

 the flat surface of the scale, like the teeth of a. "hackle." A 

 more careful examination of scales, however, of which the super- 

 ficial layers have been partly removed (c), serves to show that 

 these dark lines are but the spaces between the minute wedge- 

 like particles, arranged side by side, and end to end, of which 

 those layers are made up ; so that the structure of the scale does 

 not in reality differ essentially from the ordinary type.' Although 

 scarcely useful as a "test-object," since its structure is too easily 

 resolved, the scale of the Lepisma saccharina or "sugar-louse" 

 deserves notice ; the longitudinal ribbings being so strongly 

 marked and so regular, as to give them an appearance resembling 

 that of many bivalve shells. The long narrow scale of the com- 

 mon Gfnat, also, exhibits a few very prominent ribbings ; and, 

 from its small size, it serves as a good test-object for the medium 

 powers. 



381. The ffairs of many Insects, and still more of their larvge, 

 are very interesting objects for the microscope, on account of 

 their branched or tufted conformation ; this being particularly 

 remarkable in those with which the common hairy Caterpillars 

 are so abundantly beset. Some of these afford very good tests 

 for the perfect correction of objectives. Thus, the hair of the 

 Bee is pretty sure to exhibit strong prismatic colors, if the chro- 

 matic aberration should not have been exactly neutralized; and 

 that of the larva of the Dermestes, or "bacon-beetle," was once 

 thought a very good test of defining power, and is still useful for 

 this purpose. It has a cylindrical shaft (Fig. 282, b) with closely 

 set whorls of spiny protuberances, four or five in each whorl ; 

 the highest of these whorls is composed of more knobby spines ; 

 and the hair is surmounted by a curious circle of six or seven 

 large filaments, attached by their pointed ends to its shaft, whilst 

 at their free extremities they dilate into knobs. An approach to 

 this structure is seen in the hairs of certain Myriapods (centi- 

 pedes, gally-worms, &c.), of which an example is shown in Fig. 

 282, A. 



' 382. In examining the integument of Insects, and its appen- 

 dages, parts of the surface may be viewed either by refiected or 

 transmitted light, according to their degree of transparency and 

 the nature of their covering. The Beetle and Butterfly tribes 

 furnish the greater number of objects suitable to be viewed in 



' Podura may be obtained by sprinkling a little oatmeal on a piece of black paper 

 near their haunts ; and after leaving it there for a few hours, removing it carefully to a 

 large glazed basin, so that, when they leap from the paper (as they will when brought 

 to the light) they may fall into the basin, and may thus separate themselves from the 

 meal. The best way of obtaining their scales, is to confine several of them together 

 beneath a wine-glass inverted upon a piece of fine smooth paper; for the scales will be 

 detached by their leaps against the glass, and will fall upon the paper; and if they be 

 left thus confined for some time, they will be very likely, by treading upon some of the 

 scales, to bring them into the condition represented at c, Fig. 281, which best illustrates 

 their true nature. 



