PROCEEDINGS OF SOCIETIES. 123 



appearance, it establishes the fact that the first introduction 

 of the compound microscope was a retrograde movement. 

 About the saine time, Sir David Brewster, " after a laborious 

 examination," finds that the appearances mentioned are fal- 

 lacious, the structure of the scales being " composed of a suc- 

 cession of interlocking teeth," analogous to the fibres of the 

 crystalline lens of the eye. In 1852, or after a lapse of 

 fifteen years, the scales appear to Mr. Quekett as covered 

 with " wedge-shaped scales," which, under sufficient power, 

 may be seen " to stand boldly from the surface," and also to 

 ''project beyond the edge" of the scale. The ' Micrographic 

 Dictionary,-' 1856, under " Scales of insects," supplies the 

 following statement : — That the " longitudinal strise," of all 

 scales, " consist of elevations or ridges upon the surface, pro- 

 bably representing folds of the upper layer or membrane of 

 the scale." That in the Podura scale " the striae consist of 

 longitudinal rows of minute, wedge-shaped bodies," their 

 " darkness" being due to " refraction," and that " the other 

 more or less transverse curved strise" which ''exist upon 

 certain scales " are " wrinklings or folds of the under mem- 

 brane." Dr. Carpenter, one year later, holds yet another 

 opinion, and considers that, as in " the scaly investment " of 

 the Lepidoptera " each scale is composed of two superficial 

 colored laminae, enclosing a central laminae of structureless 

 membrane, the surface of which reflects back the light," so 

 in the Podm'a scale, "the structure does not diflPer essentially 

 from the ordinary type;" but that in those scales where 

 " the superficial layers have been partly removed " " the dark 

 lines are but the spaces between the minute wedge-shaped 

 particles arranged side by side and end to end, of which those 

 layers are made up." 



The author of the present paper considered these differences 

 of opinion to have arisen from various sources, but more es- 

 pecially from the fact that none of the writers quoted here 

 identified the scales they have described with any particular 

 species, and the only attempt that any of them has made to 

 figure the insect, occurs in the ' Micrographic Dictionary ;■" it 

 is not, however, an orginal drawing, and can only be recog- 

 nised as a species which has no scales whatever upon it. 



In the family Thysanoura there are as many as three 

 genera and seven species at least which have scales, with 

 most distinct features. But satisfactory descriptions of these 

 cannot be given without the illustrations, and they will most 

 probably be published together in future numbers of the 

 Journal. 



VOL. II. NEW SER. I 



