"^'ouhIL.dITm^^^^^ Rotjal Microscopical Socieiy. 301 
spent in vain. It may be here observed that the adjustment of the 
correcting screw of the object-glass plays an important part in 
refining the definition, independently of the thickness of the 
covering-glass. I may observe that the first six illustrations 
accompanying this paper were eft'ected by the anastatic process 
from drawings made direct from the microscope, in 1863, by a 
talented lady who is an excellent amateur painter, and who had no 
previous knowledge of the subject, and therefore wholly unbiassed. 
Fig. 3. Is a rough sketch of the Podura spines illuminated by 
direct gpudensed light. 
Fig. 4. Podura spines resolved into longitudinal striae of beads 
with the lower stria3 on the under-side of the scale partly visible. 
Fig. 5. A rather exaggerated drawing illustrative of the size of 
the beads, but correctly giving the appearances of interlacing 
lattice- work formed by the upper and under ribs of beading crossing 
each other. 
Fig. 6. Shows the careful resolution into beading by using a 
long-drawn tube: on the left the waviness of the beading is re- 
markable ; next are seen rows crossing at an acute angle, and on 
the right side a more regular display of beading running in straight 
lines. 
Distrusting at this time (1863) this novel appearance, I re- 
peated experiments hundreds of times on diff'erent scales, and 
sought earnestly for some synthetic proofs, which were finally 
found in the appearances (drawn by the same lady) caused by the 
intersections of the ribs of the finest and most transparent scales of 
azure blue " in Fig. 1, and a coarser intersection shown at Fig. 2. 
The beads to be seen brightly and clearly in the fine scales of 
Fig. 1 require very careful adjustments, and the spurious spines 
there shown, counterfeit, in every particular, the behaviour of the 
spines (which I shall also venture to call spurious) of the Podura 
scale. 
When the light is almost direct, that is, the axis of the illu- 
minating cone of rays is nearly perpendicular to the plane of the 
stage, the beads sometimes exhibit black dots, crescentic shadows, 
and brilliant points of light, according to the action of the trans- 
mitted rays upon their spherical surfaces. Similar dots may be 
seen upon the beads of the Pleurosigmata. Had we no visual 
direct proof of their sphericity, the symmetrical shifting of the 
crescentic shadows according to the direction of the light would 
prove their shape. 
I may remark that the higher the power can be raised by 
lengthening the tube and deepening the eye-piece, consistently with 
a fine definition, the better chance will be afi'orded for distinguishing 
the upper and lower sets of beads crossing each other at an acute 
angle upon the upper and lower surface of the intervening basic 
