238 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 Freshwater Ponds and
Lakes as revealed by the use of the Centrifuge.—Mr. Scourfield said
that the study of Plankton, i.e. 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 (vavvos=lwarf),
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-