“Remove some of the scales by pressing a clean and dry slide against the body of the insect, and cover them with a piece of thin glass, which may be prevented from moving by a little gum at each corner. No. 3 may then be taken as an exaggerated section of the various parts. A B is the glass slide, with a scale, C, closely adherent to it, and D the thin glass-cover. If a very small drop of water be placed at the edge of the thin glass, it will run under by capillary attraction; but when it reaches the scale, C, it will run first between it and the glass slide, A B, because the attraction there will be greater, and consequently the markings on that side of the scale which is in contact with the slide will be obliterated, while those on the other side will, for some time at least, remain unaltered: when such is the case, the strongly marked vertical lines disappear, and the radiating ones become continuous. (_See_ No. 1, the lower left-hand portion.) To try the same experiment with the other, or inner surface of the scales, it is only requisite to transfer them, by pressing the first piece of glass, by which they were taken from the insect, upon another piece, and then the same process as before may be repeated with the scales that have adhered to the second slide, the radiating lines will now disappear, and the vertical ones become continuous. (_See_ No. 2, left portion.) These results, therefore, show that the interrupted appearance is produced by two sets of uninterrupted lines on different surfaces, the lines in each instance being caused by corrugations or folds on the external surfaces of the scales. Nos. 1 and 2 are parts of a camera lucida drawing of a scale which happened to have opposite surfaces obliterated in different parts. No. 4 shows parts of a small scale in a dry and natural state; at the upper part the interrupted appearance is not much unlike that seen at the sides of the larger scales; but lower down, where lines of equal strength cross nearly at right angles, the lines are entirely lost in a series of dots, and exactly the same appearance is shown in No. 5 to be produced by the two scales at a part where they overlie each other, although each one separately shows only parallel vertical lines.” [Illustration: Fig. 204.--Outer Membrane of Upper Plane of Red Beads thrown by each alternate hole of grating; on lowering the focus white interspaces turn into blue beads.] [Illustration: Fig. 204_a_.--Outer Membrane of Lower Plane of Beads thrown from remaining holes of grating; on raising the focus white interspaces turn into red beads. Objective used, Zeiss’s apochromatic 1/12-inch oil-immersion, numerical aperture 1·40, magnifying power 1,750 diameters.]