23& 
THE ESSEX FIELD CLUB. 
‘ Survival value,’ and this lecture formed one of the sections of his work 
on Darwinism. So far as I know the Essex Field Club is the only local 
Natural History Society that can claim to have been favoured by Wallace 
with personal expositions of his views. As a rule he disliked the reading 
of ‘ papers ’ before learned Societies—even the great London Societies, 
and preferred submitting his conclusions in print to a larger and wider 
public. It will be remembered that Darwin followed the same course. 
It may not be known to many of the present members of the Club that 
Wallace was unsuccessful in his candidature for the post of Superintendent 
of Epping Forest when the Forest was formally taken over by the present 
Conservators. 
“ Had I been able to attend the meeting, I should have moved, and 
hope you will move, a resolution of sympathy with Mrs. Wallace and 
the family in their bereavement. 
" I attended the simple funeral at Broadstone as a representative of 
the Royal Society, and although I received no official mandate, I hope 
the Essex Field Club will consider that I also represented them on that 
occasion. 
“ Yours sincerely, 
“ R. Meldola.” 
Supposed unrecorded Portrait of Samuel Dale.— Mr. W. H. Dalton,. 
F.G.S., alluding to the portrait of Dr. Samuel Dale, in the Essex 
Naturalist, said that Mrs. Dalton had recognised it as being similar 
to one of four old paintings bought by her father at a sale at Braintree 
when she was a child, three of these paintings being still in the possession 
of the Everard family at Witham. Mrs. Dalton had always understood 
that one painting represented a celebrated doctor, that the lady, his 
wife, was called Judy or Judith [Judah, the first Mrs. Dale], and the others 
two of his children. The painting in Apothecaries’ Hall is of an older man,, 
but recognisable. If the pictures are really of Dale's family, they are of 
great county interest. 
Demonstration—The Nannoplankton of Fresh-water Ponds and 
Lakes as revealed by the use of the Centrifuge. —Mr. Scourfield said 
that the study of Plankton, i.c. the microscopic plants and animals which 
live suspended in the open water of the sea, lakes and ponds, had been 
going on for a good many years, collections being obtained chiefly by nets 
of the finest silk gauze. It had been recognised from the first, of course, 
that these nets, although so fine, must allow some of the more minute 
organisms to pass, but the number and volume of these was considered to 
be almost negligible. It was not until Lohmann, in 1908, introduced the 
centrifuge specially for the concentration of these exceedingly small forms, 
for which he subsequently coined the term Nannoplankton (yauuor—iwarf), 
that their importance was made apparent. 
The use of the centrifuge for the collection of small aquatic organisms 
in general was first suggested by Cori in 1895, but the method had never 
been widely adopted, most likely because it was regarded simply as a. 
substitute for the usual methods of collection by means of nets, etc. Loh¬ 
mann showed, however, that the centrifuge was indispensable so far as 
the minutest forms of plankton were concerned, and now the instrument 
was commonly used for their collection. 
As regards the methods of using the centrifuge and examining the 
nannoplankton obtained thereby, the first thing to be noted was that 
the water should be taken directly from the pond or lake into the col- 
