Royal Microscopical Society. 7 



very few. The beautiful drawings illustrating tlie paper in ' The 

 Student ' for last February, to which allusion has already been 

 made, strike me as being faithful representations of these pigment 

 granules. I take exception, however, to those showing beads in the 

 Podura scales, for these seem to me to represent in an equally 

 satisfactory manner, the " ghost-beads " I have spoken of above. 



Thus, provided others can confirm my observations, the exist- 

 ence of two causes of beaded appearances has been traced in extreme 

 cases ; but how far, in some scales, either of these causes prepon- 

 derates over the other, will be, I believe, a puzzle to microscopists 

 for many a day to come.* 



But we are not done with the scales of insects. There yet 

 remains another feature to be briefly alluded to, namely, the modifi- 

 cations of the folds or corrugations of the membranes themselves. 

 In some scales (see the figm-e of the scale of the larva of Attagenus) 

 the corrugations are such that the surface presents longitudinal 

 grooves and ridges only. In others (and by far the greater number 

 are of this pattern), a second set of corrugations crosses the primary 

 set at right angles, breaking up the surface into embossings with 

 rounded-off edges.f 



In order of importance this feature should be spoken of first, 

 since it is that which gives the primary character to the scale ; but 

 as due prominence has been given to it in a former paper, it wiH 

 not be necessary to dwell at much length upon it here, particularly 

 as a more extended examination of the scales of insects has tended 

 to strengthen me in the views I there expressed, rather than to 

 alter them.t 



To illustrate the three features which I have endeavoured to 

 enumerate, as puzzling us in our examinations of insect-scales under 

 high powers, I have selected an accidental experiment, which I 

 thought so curious, as to make a drawing of on the spot. I had 

 been mounting some slides of the scales of Petrohius maritimus, 

 and noticed in some of the slides that the cement ran in under the 

 glass cover. Several of the scales confined a bubble of air between 



* It may be that these pigment granules often exist in the membranes of scales 

 in an almost colourless condition. I believe they are almost imiversally present 

 in the membranes of highly-organized scales, such as those of the Lepidoptera ; 

 and the only scales where I have been unable to discover them myself are those 

 of the Thysanura, making exception, however, to the scale of Petrobius, which 

 presents much similarity to the scales of many Lepidopterous insects, and in which 

 they exist beyond a doubt. It does not follow, however, that because I have not 

 been able to convince myself of their presence in Lepidocyrtus, Sena, and Temple- 

 tonia, that therefore they are absent in those genera. 



t Not always rounded off, however ; sometimes they form rectangular divisions 

 in the scale. (See Dr. Maddox's note appended to this paper. He deals with this 

 portion of the subject more thoroughly tlian I do.) 



X It will he recollected that, in that paper, I made exception for the existence 

 of pigment and mdescerice, which needed a more complete examination than I 

 could tliea make, eie I could comment on Dr. Pigott's paper, read the same even- 

 ing as mine, and with the contents of which I was previously quite ignorant. 



