*jounlai,*JaTifMa '] ^oijol Microseopiccd Society. 5 



According to the nature and direction of the illumination so the 

 view of the markings is greatly changed, and it would he quite 

 impossible except by the aid of photography satisfactorily to repre- 

 sent all the appearances it is possible to obtain.* I have chosen one 

 view for representation (obtained by illuminating from below the 

 stage at a wide angle), in which some idea of the real structure of 

 the surface of the scale and the relation of the markings to each 

 other, according to my opinion, is attempted to be shown. (See 

 Fig. 6.) 



To sum up, then. I do not believe that the Podura scale con- 

 sists of globular beads placed at pretty regular intervals between 

 two membranes. I believe it to be a case of " one apparent excep- 

 tion proving a rule," and that rule is, that the markings of the scales 

 of insects, except where iiidescence or the presence of pigment claims 

 attention, are wholly due to corrugations of the membranes. 



So far as I can judge, I believe both sides of a Podura scale are 

 alike, and I have examined the scales uncovered as opaque objects 

 with high powers. This proceeding is very difficult, and not wholly 

 satisfactory, but I think I have seen enough to form an opinion 

 upon it. I have never been able to separate a Podura scale into 

 upper and lower laminae ; but there is every reason, I think, to believe 

 that, as with the scales of other insects, there are two. For instance, 

 in the scale of the Diamond Beetle [Eupliolus), when detached and 

 viewed by transmitted hght, one lamina is seen to possess the 

 iridescence and the other is transparent; and it has happened to 

 me in endeavouring to obtain the scales from the wing of a species 

 of Morpho in my possession, that single scales have been split, one 

 lamina, the upper one, which readily comes away, being strongly 

 corrugated and nearly translucent, and the other, which it was not 

 so easy to detach from the wing, being intensely blue, and possess- 

 ing extremely minute longitudinal striae. 



* This remark is equally true with regard to all the Podura scales, as Mr' 

 Beck's figures of tlie scale of Lepiclocyrtus testify. 



