PROCEEDINGS OF THE SOCIETY. 
691 
tenths, and hundredths of a millimetre. Critical micrometric measure- 
ments had been made of this plate, and it was found to be accurately 
and evenly spaced — and in brief was one of the best micrometers he 
had ever handled. It, like the others, was mounted in realgar. The 
gift of these beautiful micrometers to the Society would, he was sure, 
be much appreciated by the Fellows who would now have in their 
cabinet two accurate micrometers for the purpose of comparison. The 
other two were test-plates, the first of which had twelve bands varying, 
with intervals of 5000 lines, from 5000 to 60,000 lines per inch. The 
other contained ten bands varying, with intervals^ of 200, from 200 to 
2000 lines per millimetre. These also were mounted in realgar. 
The second portion of Mr. Grayson’s packet consists of test diatoms 
mounted in realgar, the following being some of the species : — Pleuro- 
sigma angulatum , P. elongatum, P. balticum , Frustulia saxonica, Navicula 
rhomboides , Pinnularia nobilis with hoops, and Amphipleura pellucida. 
Specimens of N. rhomboides and Pinnularia were also mounted in 
sty rax for the purpose of comparison. He might mention in passing 
that the A. pellucida slide contained also an interesting Nitzscliia , the 
resolution of which was more difficult than that of A. pellucida. The 
packet was received just after their last meeting in June, so that the 
slides had been here during the hot summer, and they had also stood 
the heat and rough handling in the post from Melbourne, and as yet 
showed no signs of crystallisation, and Mr. Grayson said that from the 
method adopted there was no fear of this taking place ; if so, a great 
desideratum had been accomplished. A specimen of ruling suitable 
for a diffraction grating was included in the packet. 
He had great pleasure in moving that the very hearty thanks of the 
Society be given to Mr. Grayson for his very useful presents. Put, and 
carried by acclamation. 
Mr. J. Hewton Coombs’s paper, ‘ The Reproduction of Diatoms,’ was 
read by the Secretary, and was illustrated by a series of lantern slides. 
Mr. A. W. Bennett, in response to the President, said that not being 
a diatomist, he rather shrank from saying anything upon the subject. 
The study of diatomy had gone through three stages : in the first, these 
organisms were brought under notice by microscopists because of the 
extreme beauty of their siliceous forms, and their uses as tests for the 
powers of the Microscope ; then followed their classification, and the 
determination of species, and with this the excessive multiplication of 
species which was so greatly to be deprecated ; and then came the study 
of these forms with a view to the determination of their life-history. 
It was very remarkable, however, notwithstanding all that had been 
done, how very much they had yet to learn as to the life-history of the 
diatoms. In the writings of Smith, Thwaites, and others of the older 
diatomists, they found a few observations on their life-history ; but with 
these exceptions, very little had been determined on this point till within 
the last few years. It is a familiar fact that many of the lower vegetable 
organisms multiply in two different ways, by a sexual and a non-sexual 
process, the non-sexual mode being often the result of an abundant 
supply of nutriment, the sexual mode of a deficiency in this respect. 
There can be no doubt that diatoms multiply in both ways. The paper 
