THE ESSEX FIELD CLUB. 227
then engaged in devising and perfecting.1 Nothing more beautiful and instruc-
tive than the slides of Sabella, Aurelia, Ophiura, or that of a young plaice, with
the aorta and arteries filled with blood, could be desired, every detail of
structure being wonderfully retained. He also showed specimens well-pre-
served in "Formalin" (Formic-Aldehyde), especially the fairy-like Cydippe,
which is often so common in the estuary.
Dr. Sorby further exhibited samples of solutions of colouring-matters
extracted in the simplest way from Marine Algae. The plants were placed in
fresh-water, which quickly dissolves out the colouring-matter. The solution
having been filtered, sugar is added to the saturation-point, in order to
prevent decomposition. One of the most beautiful colours thus extracted
showed the phenomena of fluorescence in a high degree, the solution being
of a deep orange tint by reflected light, and a beautiful pink tinge by trans-
mitted light. He also read a "Note on the Food of Oysters in Essex"
(ante, p. 169.)
A hearty vote of thanks was passed to Dr. Sorby at the conclusion of his
papers and exhibits, on the motion of the President, who said that such work
was an example of the source of real progress in knowledge of marine life.
Mr. W. M. Webb, F.L.S., showed the original shells from which the
"sciagraphs" reproduced on Plate iii. of vol. vi. of the Journal of Malacology
had been taken for the purpose of proving the value of the Rontgen-rays in
the study of Conchology, points being brought out which could not otherwise
be clearly demonstrated without cutting or sectioning the shells. The
majority of the specimens formed a series showing the evolution of the
Cowry-shell (Cypraea arabica) from a spiral, thin-lipped form to the well-known
covering of the adult. Mr. Webb pointed out how, through the incurving of
the lip and the formation of one row of "teeth" on its edge and another on
the body-whorl opposing the first, the peculiar entrance to the shell was
formed ; and again, how through the laying down of a considerable amount
of pearly material and colouring-matter on the outside of the shell, by the
mantle-lobes, which can be protruded to meet on its dorsal middle-line, the
original colouration is hidden, and the more massive shape is arrived at.
Another feature of the exhibit was the rendering visible of the clausium or
shelly plate attached to the inside of the shells of the terrestrial Clausilia and
which closes the entrance on the withdrawal of the animal after the manner
of a door.
Mr. Webb also exhibited a specimen of Crepidula fornicata, a native of
Rhode Island, U.S.A., which was attached to a foreign oyster laid down at
Brightlingsea and which had, of course, been imported with the oyster.2
In the absence of Dr. Laver, who was announced to read a paper on the
"Colne Oyster Fisheries; their history and methods," Mr. J. C. Shenstone
gave some details on the subject. The substance of Mr. Shenstone's remarks
will be found in the abstract of his address at the meeting at St. Osyth and
Brightlingsea, September 7th, 1891 (see Essex Naturalist, vol. v., pp. 257-58).
1 See Dr. Sorby's paper "On the Preparation of Marine Animals and Plants as Trans-
parent Lantern-slides '' in the Commemoration Volume of University College, Sheffield.
2 See Mr. Crouch's paper on the occurrence of this species off the coast of Essex, in
Essex Naturalist, vol. viii, pp. 36-38.