32 Opaque Objects with High Powers. By G. W. Moorehouse. 
spines of the Podura scale. It must be remembered that these 
three insects are very closely allied. That Podura scales are really 
armed with projecting spines I consider as proven by the experi- 
ments of Dr. Arnold, of New York, a few years ago ; but if any 
further proof was needed, the demonstration is complete by this 
method of illumination. Both on the scales of the American 
Podura and the British Lepidocyrtus Podura, the spines are seen 
distinctly projecting anywhere on the surface of the scale, and also 
over beyond the end of the scale farthest from the body of the 
insect. The inference would appear to be that the scales are un- 
developed hairs, and the spines secondary hairs, and that the latter 
are in some species modified, or imperfectly developed, so as to form 
ribs. 
Of the many diatoms examined I only mention one, the Pleu- 
rosigma angulatum. Some of the specimens of this test were 
mounted by Moller, and others by Wheeler. All are seen in hex- 
agons, and with great distinctness ; not, however, surpassing results 
obtained by other illumination. I send with this communication a 
slide of broken specimens of a coarsely marked variety of this 
diatom, found in Nottingham earth. I think it will readily be seen 
that the line of fracture runs through the hexagonal areolae, often 
leaving the points of the network projecting. The vertical 
illuminator confirms this idea of the structure. It will be noticed 
that some of the fragments of Angulatum on this slide are split 
into two layers or plates ; the two plates are quite distinct, and the 
line of fracture of each may be easily traced in some of the pieces. 
With the T V, and a Yincli eye-piece, with either the opaque 
illuminator or an objective used as an achromatic condenser, the 
edges of the fractured specimens are clearly defined. Although 
the Angulatum is made up of two plates like Coscinodiscus, the two 
plates are much nearer alike than they are in Coscinodiscus. 
The coarsely marked diatoms are displayed with great beauty 
under this reflected light, and one can have but little doubt in 
regard to their true structure ; and this in a still greater degree is 
true of insect scales. On the whole, then, opaque illumination, 
with high powers, cannot be said to be a failure, but, on the con- 
trary, almost or quite keeps pace with the easier problem (as far 
as construction of accessories is concerned) of illumination by trans- 
mitted light, and proves itself a valuable aid, even when the most 
difficult and strongly controverted questions are attacked . — A paper 
read before the Dunkirk (U.S.A.) Microscopical Society. 
