^Smai.1iec'ri869*'] ^oyd MicTOSCo^ical Sociehj. 303 
0. The translucent ribbing of Lepisma SaccJiarina is formed 
of regular beads, and beneath these and radiating from 
the quill are hnes of smaller beading crossing the upper 
set in straight lines. I see these yellow-green, whilst 
the upper set are brownish red. 
T>. By gas-light I observed rows of red spherical beads, placed 
upon the surface of the test-object, marked by the pre- 
parer of the scale 8. H{^poca7npus* alternating with 
yellow-green rows, somewhat encroached upon by the 
# upper sets ; all running parallel to the axis of the scale. 
4000 diameters. 
E. The surface of metals and alloys, with a power of 1000 
diameters, shows, under reflected light, particles appa- 
rently spherical, agglomerated together, with dark lines 
separating the particles. 
N.B. — Diffraction-rings similar to those observed about minute 
stars are abundant for single particles (scattered on paper by gild- 
ing) in proportion as the spherical aberration is less perfectly 
corrected, but which disappear when the aplanatism is established. 
Query. — Are the diffraction-rings of stars due to the undulatory 
theory of light, or to the residuary uncorrected aberration of tele- 
scopic object-glasses ? 
Note. — The perfect definition of a broken surface of metal is a 
more severe test of aplanatism than artificial globules of mercury. 
I may now, perhaps, be permitted to present to the Koyal 
Microscopical Society synthetic evidence of the structure of the 
Podura, which appears to me to satisfactorily account for the pecu- 
liar, and I may say, embarrassing phenomena attending the study 
of the minute structure of this precious scale. 
I beg particularly to call attention to Figs. 1 and 2. A careful 
search with a power of 150 among the scales of Folyommatus Argus, 
or Azure Blue, always found among the Battledore scales, of which, 
indeed, there are several kinds, will be rewarded with appearances 
which present the characteristic waviness or watered-silk appearance 
so peculiar to the Podura scale under low powers. These draw- 
ings, made in 1863, elucidate the cause of the Podura markings. 
With high powers, as 1000 to 2000, these scales show similar 
beading, and we have here a perfect example of a spurious spine 
being formed by lines of interference and diffraction ; the beading 
being obliterated in the blank spaces, and dark markings or spines 
presented, precisely as is the case in the celebrated Podura scales. 
To my own mind this synthetic formation of the Podura markings 
IS perfectly satisfactory and conclusive. 
* This diatom is a specimen of Pleurosigma Strigosum. 
