NOTES ON THE STRUCTURE OF THE DIATOMACE#. 7I 
NOTES® ON VGHE STRUCTURE OF “TRE 
DIATOMACE:. 
Biv biupRIGE SiS- 
HERE have been in many scientific journals, from time to time, 
notes upon the structure of the Diatomacez ; many persons 
have ventilated their opinions, some have given drawings, others 
photographs ; but nothing is yet decided upon the subject. 
I do not think that I can do much in that way, but wish to 
record a few observations of my own; and also, some original 
drawings (unpublished), supposed to be by Dr. Walker Arnott, 
having been found by myself in a book of his in the Glasgow 
University. Papers on Diatomacez, Vol. 3; article, “ Rylands on 
Markings of Diatomacez,” on the margin of the second page, 
copied by permission of J. B. Balfour, Esq. 
One of the earlier remarks on Structure is by Shadbolt, Trans. 
Fig. 25. 
Micro. Soc., 1849 (Vol. 3, p. 49), proving that a frustule of 
Arachnoidiscus consists of four discoid portions, and of two 
annular valves (connectives) in which he is followed by F. Kitton,* 
and C. Stodder.t This may also be seen in Heliopelta, and in 
Coscinodiscus oculis tridis. W. Pring{ has made sections of the 
latter diatom in question, by slicing thin rock sections of diatomi- 
ferous rock, from Nykjobing, Jutland (Cementstien), showing that 
the diatom is covered with a reticulated design,—the result of the 
super-position of two layers (Fig. 25). The upper part, formed of 
hexagonal cavities, resembling the alveoli in a honeycomb, and the 
lower, composed of small areolz, convex according to some, con- 
cave according to others, placed each in the centre of one of the 
hexagonal depressions. I have also the same diatom in a diatoma- 
* O.J. Mic. Stud. (Vol. 8), N. 5, p. 15, and Sci. Gos., 1877, p. 65. 
+ Lens. Chicago, 1872, p. 3. + Ann. Soc. Belg. Mic. mem. vii., 1880. 
