OF MICROSCOPIC OBJECTS. 51 



from still more minute insects, as the podura, scales are taken 

 which were at one time esteemed as a most delicate test. The 

 gorgeous colours which the diamond beetles also show when under 

 the microscope are produced by light reflected from minute scales 

 with which the insects are covered. 



In mounting these objects for the microscope it is well to have 

 the part of the insect from which the scales are usually taken as 

 a separate slide, so that the natural arrangement of them may be 

 seen. This is easily accomplished with the wings of butterflies, 

 gnats, &c. ; as they require no extraordinary care. In mounting 

 the scales they may be placed upon slides, by passing the wings 

 over the surface, or by gently scraping the wing upon the slide, 

 when they must be covered with the thin glass. Of course, the 

 extreme tenuity of these objects does away with the necessity of 

 any cell excepting that formed by the gold-size or other cement 

 used to attach the cover. The scales of the podura should be 

 placed upon the slide in a somewhat different manner. This insect 

 is without wings, and is no longer than the common flea. It is 

 often found amongst the sawdust in wine-cellars, continually leap- 

 ing about by the aid of its tail, which is bent underneath its body. 

 Dr. Carpenter says : " Podurse may be obtained by sprinkling a 

 little oat-meal 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 be- 

 neath a wine glass inverted upon a piece of fine smooth paper ; 

 for the scales will become detached by their leaps against the 

 glass, and will fall upon the paper." These scales are removed 

 to the slide, and mounted as those from the gnats, &c. When 

 the podura has been caught without the aid of the meal, it may 

 be placed upon the slide, under a test-tube, or by any other mode 

 of confinement, and thus save the trouble of transfer from the 

 paper before mentioned. Another method is to seize the insect 

 by the leg with the forceps and drag it across the slide, when a 

 sufficient quantity of scales will probably be left upon it. 



These scales are usually mounted "dry;" but Hogg recom- 



