ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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seen in this photograph, the lower membrane which is beneath not being 
visible. My clerk omitted the two words “ at least,” thus completely 
altering the sense and placing me in contradiction both with the state- 
ments in my Synopsis, published in 1885, and with the note on the 
‘Structure of Diatom Valves’ which I recently sent to the Royal 
Microscopical Society, in which I everywhere admit the existence of 
three layers.” 
New Photograph of P. angulatum, by Dr. H. van Heurck. — At 
the March meeting of the Society a photograph, by Dr. H. van Heurck, 
was exhibited of P. angulatum, produced with Zeiss’s apochromatic 
objective of 1 * 6 N.A., in further elucidation of Dr. van Heurck’s views 
on the structure of diatom valves. 
The note accompanying the photograph was as follows : — 
“ I have the honour to submit to the Royal Microscopical Society a 
photograph of P. angulatum, made with the objective of 1 • 6 N.A., using 
strictly axial illumination. The fracture of the upper edge shows clearly 
that the “ beads ” are holes in the intermediate layer, and that the form 
of these holes (beads) is hexagonal, as maintained by Mr. Smith and 
myself. The form of the small bar on the extreme top, which is the 
part of the negative focused, shows that the “ beads ” cannot be round.” 
The Formation of Images in the Pleurosigma formosum. — Mr. E. 
M. Nelson communicated the following note to the Society at the 
meeting of the 19th March: — “It was stated at the January meeting of 
the Royal Microscopical Society that it was impossible to produce images 
in the markings on a P. formosum. Some years ago it was said that 
images formed by the primary structure of coarse diatoms, such as 
Triceratium and Coscinodiscus, proved that the markings were lenticular. 
With this opinion I did not agree, and was led to investigate the subject. 
I not only confirmed the experiment with regard to the coarse diatoms, 
but eventually succeeded in producing images in the P. formosum, I 
also produced images in minute holes punctured in a piece of tinfoil. 
This latter experiment shows that the production of images in diatom 
markings does not prove that they are lenticular. I have now made a 
photomicrograph of a F. formosum with images formed in the markings 
X 2000. The images might have been made more distinct had more 
time been expended on the photomicrograph.” 
