Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature . cover the scalesthey put up with the thinnest possible glass, so that,when opportunity offers for an examination of theslide under a remarkably good -^th or TVth, theymay not find themselves doomed to disappointment,owiug to the inability of the objective to penetratethe thick cover. In conclusion I beg to offer a few remarks onthe scale of the Speckled Podura. As I havestated above, it possesses transverse striae, andthese are rendered most distinct when the centralrays of the achr
Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature . cover the scalesthey put up with the thinnest possible glass, so that,when opportunity offers for an examination of theslide under a remarkably good -^th or TVth, theymay not find themselves doomed to disappointment,owiug to the inability of the objective to penetratethe thick cover. In conclusion I beg to offer a few remarks onthe scale of the Speckled Podura. As I havestated above, it possesses transverse striae, andthese are rendered most distinct when the centralrays of the achromatic condenser are stopped believe that the structure of Podura scales ingeneral may be best studied in this one. From verycareful examinations I have no doubt that the March 1,1867.] HARDWICKES SCIENCE-GOSSIP. 59 surface is uneven, and believe that its irregularity isthe result of both upper and lower membranesbeing folded into a number of minute pleats orwrinkles, which have a tendency to overlap eachother—a difference in detail only, not in plan,between these markings and those on the scales of. Fig. 50. Scale of Podura, unknown species, x 450. all other insects. This is best shown by obliqueillumination; but when the illuminating ray is in adirection corresponding to the axis of the micro-scope the appearance is totally changed, and thewedge-shaped markings, which I believe to behollows between the pleats or corrugations (andnot particles, as stated in the MicrographicDictionary and elsewhere), come into view dark outlines, I think, represent the shelv-ing sides of the little pits, and the bright space inthe centre of each is the deepest portion, whichfrom its position with regard to the ray, obstructsthe least amount of light. By moving the diaphragms of Powells condensera little backwards and forwards, so as to obtainalternately direct and oblique light, the appearancesrepresented in the figure attached are given. Theconclusion I have arrived at s
Size: 1447px × 1726px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectscience
