Ilhe Advancing Poiven of Microscopic Definition. 61 



collis are very similar iu structure, the markings on the Lepidocyrtus 

 being the finest. These scales probably consist of a double membrane, 

 and the markings are probably corrugations in these membranes. 

 The corrugations on the opposite sides of the scales differ in boldness, 

 those on the side next the insect being most prominent. If this side 

 is towards the objective the exclamation marks are seen as the objec- 

 tive approaches the scale, before the varicose ribbings of the two 

 membranes come distinctly into focus. In the reverse position of 

 the scale the varicose ribbings are first seen, and the exclamation 

 marks do not become distinct till after the scale is focussed through. 

 The corrugations appear to have the form of narrow, longitudinal 

 somewhat wavy ribs, which are constricted at short intervals, giving 

 them a varicose aspect (Dr. Pigott's ' beads '). The ribs on the 

 opposite sides cross each other at a small angle, and in this circum- 

 stance, and the different degree of prominence belonging to the mark- 

 ings of the opposite sides, the true explanation of the exclamation- 

 mark appearance must probably be sought. These exclamation 

 marks are probably illusive or spurious appearances, notwithstanding 

 the great distinctness they attain under favourable conditions of 

 illumination." 



The photographs, the Colonel informs us, represented a magni- 

 fying power of 3200 diameters ; central light showing the exclama- 

 tion markings, and oblique illumination the varicose or beaded 

 appearances. 



Our talented and distinguished Secretary, Mr. Slack, who is well 

 known for the strength of his convictions, in the ' Popular Science 

 Review ' for January, 1872, recurs to the same subject in an elaborate 

 paper, apparently with the honest intention of setting this matter 

 at rest. " The scales of insects," says this gentleman, " are an orna- 

 mental covering, probably of some use in protecting the membrane 

 from which they spring, and on which we find them arranged like 

 tiles on a roof; but the flying power does not seem impaired when 

 numbers of them are rubbed off. By their beautiful aspects, they 

 make, according to Mr. Wallace's observations, males and females 

 mutually attractive, and they are frequently the means of disguises 

 which enable their possessors to escape notice of their enemies." 

 He goes on to remark that 



" Among the most difficult to be shown clearly, are certain mark- 

 ings on the scales of insects popularly termed Podura ; and since 

 Dr. Pigott affirmed that in the famous test-scale now named Lepido- 

 cyrtus curvicollis, with sufficiently corrected glasses a distinctly 

 beaded structure was to be seen in them, fresh discussion as to their 

 real nature has gone on without ceasing, and strong feelings, as well 

 as reasonings, have been shown by many who had perfectly satisfied 

 themselves with the appearance of the well-known note of exclamation 

 marks, so well shown and so beautifully figured by the late Kichard 

 Beck." 



V 2 



