ON MICROSCOPIC DISCOVERY. 



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strong longitudinal fibres, from whose sides 

 proceed a number of spines much resembling 

 those in fig. 4. These spines form, we be- 

 lieve, the diagonal lines in other and more de- 

 licate scales, such as the podura ; for by vary- 

 ing the illumination arid moving the object, 

 we can discover in the lepisma all the ap- 

 pearances which perplex the observer when 

 examining the podura and brassica. And, 

 indeed, it is a fair inference that these minute 

 scales have great similarity of structure, and 

 that those most easily developed may justly be 

 taken as an index to others more difficult of 

 examination, when, as in the present case, 

 there is nothing to contradict the analogy. Mr 

 Pritchard seems to hold opinion with us; for 

 he re marks, in his List of Microscopic Objects, 

 " In my best engiscopes, under certain il- 

 luminations, the markings (of the podura) ap- 

 pear detached, like short hairs or spines cover- 

 ing the delicate tissue of the scales." The 

 high authority of Sir David Brewster is, how- 

 ever, opposed to our explanation of the pheno- 

 mena of the tests; and we deem it proper to 

 give his theory as a necessary check upon our 

 own. 



" After a laborious examination of the lined 

 tests, and the use of every optical resource 

 which he could command, Sir David Brews- 

 ter has found that the mysterious lines on these 

 test objects are only apparent lines, being com- 

 posed of a succession of interlocking teeth, by 

 which the fibres to which they are attached 

 form that delicate film that composes the scale I 

 of a moth." This is Sir David Brewster's 

 opinion regarding the luigitudinal striae ; and is 

 the result of his examinations into the struc- 

 ture of the crystalline lenses of fishes. " With 

 regard to the diagonal or oblique lines," it is 

 added, " which have been such a source of 

 perplexity to microscopical observers, we have 

 little hesitation in pronouncing those which we 

 have seen to be optical illusions, from the acci- 

 dental aliynement of the sides of the teeth in dif- 

 ferent grooves, when similarly illumined by 

 oblique rays. When the scales are immersed in 

 diluted sulphuric acid, we have never seen the 

 diagonal lines. When the sulphuric acid is too 

 strong, the scales curl up, and often in this 

 state exhibit the lines very beautifully. We 

 have observed diagonal lines singularly deve- 

 loped in the laminae of the crystalline, and 

 clearly arising from the interference of the 

 rays acted upon by the lines on one side of the 

 laminae, with the rays acted upon by the 

 lines on the other side, and therefore we have 

 been the more confirmed in our opinion." 



Fig. 14. Scale of the menelans butterfly. This 

 object consists of a fine tissue overlaid with 

 strong and well defined lines. The latter are 

 frequently detached from the membrane, as 

 shown in our specimen ; and consequently, 



there can be no illusive misconception regard- 

 ing these lines, which are evidently fine fibrous 

 cords in relief, upon the surface of the scale. 



Fig. 15. This is a very singular scale, 

 observed amongst a miscellaneous group. The 

 longitudinal striae are strongly defined, and 

 the cross markings arise from a contraction, 

 or shrivelling up, of the membraneous part 

 between each two of the striae. 



Fig. 16. Scale of the azure blue butterfly. 

 The light coloured and most diaphanous scales 

 of this species form beautiful test objects for 

 the microscope. The striae are delicate, but 

 are easily developed by a good doublet. 



Fig. 18. Scale of the lepisma. The strias on 

 this object are easily defined, and they have 

 the same character with those on the scale of 

 the menelaus, as is evidenced by the partial 

 detachment of the lines from the membrane- 

 ous tissue. There is a variety in these scales : 

 the one we have selected, and on which the 

 markings are more delicate, is nearly oval- 

 shaped ; but there are others much resembling 

 a shell, and having the upper edge scalloped 

 very regularly. Diagonal markings are per- 

 ceptible on the latter species, produced by 

 undoubted spiny projections from the longi- 

 tudinal fibres. 



Fig. 19. Scale of the diamond beetle. The 

 elytra, or wing case, of the diamond beetle is a 

 splendid opaque object, familiar to every pos- 

 sessor of a microscope. We may compare 

 the appearance it presents to that of the ancient 

 Jewish breastplate ; a number of small cavities 

 regularly disposed over the surface, are filled 

 with a vast number of small scales, which re- 

 flect every variety of hue, and exhibit a lustre 

 and magnificence that dims the splendour of 

 the most richly arranged jewellery. Our 

 figure shows one of these minute scales, with 

 its semi-opaque spots and striae ; the latter, it 

 will be noticed, have precisely the same char- 

 acter with figs. 10. and 1 1. 



Fig. 20. The scale of a moth. This object 

 is very opaque compared with preceding ones, 

 and it is consequently difficult to trace its 

 structure with much precision. The contour, 

 it will be seen at once, is that of a leaf; and 

 the vegetable analogy would seem to extend 

 much further. This scale appears to consist 

 of a fibrous frame- work, resembling very much 

 the skeleton of a leaf; and the interstices are 

 filled up with a mossy substance, whilst the 

 prismatic reflections and other characteristics 

 of the surface would indicate that smaller scales 

 are scattered over it. 



Fig. 21. Disposition of the scales. This is 

 a small diagram, intended to convey an idea 

 of the disposition of the scales on the mem- 

 brane of a butterfly's wing. The double 

 lines of points mark the places where the 

 scales are inserted; and it will be noticed, 



