358 
NOTES AND MEMORANDA. 
The Atlas lip to the present date contains 2230 figures illustrating 
the following genera : — 
1. Actinoptychus .. 
Flgvires in 
Atlas. 
. .. 41 .. 
Species in 
Habirshaw’s Catalogue. 
62 
2. Amphora 
- .. 3G9 .. 
196 
3. Asteromphalus .. 
. . . 24 . . 
34 
4. Aulacodiscus 
. .. 64 .. 
55 
5. Auliscus 
. .. 75 .. 
46 
G. Campylodiscus .. 
. .. 19G .. 
115 
7. Cocconoma 
. .. 35 .. 
.35 
8. Coscinodiscus 
. .. 218 .. 
129 
9. Cymbella 
. .. 79 .. 
119 
10. Encyonema 
. .. 34 .. 
19 
11. Navicula 
. . . 87G . . 
.. 830 
12. Surirella 
. .. 219 .. 
221 
2230 .. 
.. 1861 
In the above table we have compared the number of figures in 
each genus with the number of species in Habirshaw’s Catalogue. It 
will be seen that in most cases the figures are much in excess ; but on 
comparing the names in the descriptions of the plates, we find the 
actual number of species figured is much below that in the Catalogue ; 
for example, in the genus Actinoptychus we have 41 figures repre- 
senting 23 species; Aulacodiscus, 64 figures, 24 species. A large 
proportion of the generic (330) and specific (6186) names in the 
Catalogue are only synonyms ; but estimating the actual number of 
genera at 150, if the work is continued on its present scale, it will 
require 200 parts to complete it, and its publication will extend 
to fifty years. 
Application of Freezing Methods to the Microscopic Examination of 
the Brain. — Mr. Bevan Lewis, F.R.M.S., contributes the following 
(with additional matter) to ‘ Brain ’ — “ Our handbooks teem with 
descriptions of the most approved methods of preparation by harden- 
ing reagents, but I cannot recall to mind any description of the 
method to be adoj^ted for examining the brain in sections obtained by 
freezing, and I therefore purpose describing the method adopted by 
myself, feeling convinced that it will be fully appreciated by those 
who have up to the present employed the tedious process of chrome 
hardening, and suffered, as I have iiersonally, from the numerous dis- 
appointments attendant upon the exclusive use of this method. It 
appears to have been the opinion of several microscopists who have 
employed the chrome salts exclusively, that the freezing method was 
wholly inapplicable to the investigation of the central nervous system, 
and several authorities in cerebral histology had expressed to me such 
an opinion. Results obtained by at least one German observer and 
my own work at the West Riding Asylum prove this view to bo 
incorrect. 
I was led to the employment of ether for freezing tissues, after 
having experienced numerous difficulties in the use of the ice and 
* ‘ Brain,’ vol. i. 
