ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
425 
of the sun’s image received from the small mirror in a northerly direc- 
tion (fig. 54). 
The mode of using the instrument is as follows : — Set the base as 
marked to the true north, level base, set small mirror to latitude as 
engraved on the arc at side of clock, and adjust this mirror to throw 
an image of the sun upon the centre of the larger mirror ; if the photo- 
micrographic apparatus be also placed due north and south, this image 
will be reflected through the Microscope to the focusing screen of 
camera or sensitized plate, whichever is in position. 
Brass caps to protect the mirrors are provided. 
Photomicrography of Podura-scales. — The following is the sub- 
stance of the Hon. J. G. P. Vereker’s remarks when exhibiting his 
preparations at the meeting of the Society on December 16th, 1891 : — 
“ I have been lately experimenting in photomicrography upon some scales 
of Podura, and have obtained results which seem to throw some light 
upon the structure of this difficult object. 
The prints exhibited are from the negatives which I have obtained, 
and they appear to prove that the Podura-scsilo consists of a hyaline 
beaded membrane, having minute featherlets inserted in it as described by 
Dr. Edmunds in his paper to your Society.* 
The photograph taken by Zeiss 4 mm. apochromatic lens gives a 
magnification of 480 diameters, and shows two different resolutions, one 
the well-known “exclamation” marks, and the other the scale covered 
with minute featherlets, which seem to stand out above the surface ; it 
was on this latter resolution that the final focusing was done. To test 
this resolution, I took a photograph of a scale with dark-ground resolu- 
tion, using for this purpose an immersion paraboloid, as shown to mo 
and others by Dr. Edmunds, some years ago. For this purpose I used 
a water-immersion of Nachet’s .No. 9 (about 1/13 in.), and this photo- 
graph seems clearly to show that they stand out above the basement as 
minute featherlets with a forked end, There is an indication of mark- 
ings on their surface and a central midrib appears in some of them. I 
have tried to get further resolution of these featherlets by means of a 
1/12 in. oil-immersion of Reichert’s, but have failed, though the 
appearances would seem to indicate markings like a simplified Lepisma 
scale. 
The standing up of the featherlets, as we may call them, is well 
shown under dark-ground illumination, as in this method the scale itself 
acts as the light radiant, showing the scale brightly illuminated on a 
black ground. 
I also exhibit a photograph of a fine scale of speckled Podura, 
kindly lent to me for this purpose by Dr. Edmunds ; it is taken by 
direct illumination with a 1/12-in. of Reichert’s, N.A. 1'25, and is 
magnified about 900 diameters. It shows the beaded appearance of the 
hyaline base membrane of the scale. These markings exist in both 
Podura plumbea and speckled Podura, but are more strongly developed 
in the latter scale. The structure of the base membrane seems to be 
such that at the broadest part of the scale there are one or two rows of 
beads between the featherlets, whilst towards the base and top of the 
This Journal, xviii. (1877) p. 85. 
