Journal of Proceedings. xiv
So far no data had been placed on record concerning British species of
Hydrachnids. Mr. Saville Kent had, however, succeeded within the
course of two summers, 1868 and 1869, in collecting upwards of fifty
varieties within the neighbourhood of London, and upon such a sub-
stantial foundation hoped soon to be in a position to make a first report
upon the indigenous species. The assistance of the members of the
Essex Field Club in working out the Hydrachna fauna of the Epping
Forest district was earnestly solicited.
Mr. Kent illustrated his remarks by the exhibition of living and pre-
served specimens of numerous species under the microscope (including
ova, hexapod larvae and adults), and a number of exquisitely-coloured
drawings. Many of the preserved specimens, although prepared as long
as fourteen years ago, still retained their original brilliant colouring.
The medium employed for their preservation was, in most instances, a
weak solution of alcohol, i. e., one of spirit to four or five of water. The
lifelike extension of the limbs notable in all the specimens exhibited was
accomplished by the momentary immersion of the animals in boiling-
water. For arriving at a correct knowledge of the characters of the oral
apparatus, with the accompanying palpi and mandibles, it would be
necessary to crush or dissect examples, and mount the parts as trans-
parent objects in balsam.
The President initiated a short discussion on the mode of development
and ecdysis or shedding of the skin in the larval forms of the Hydrach-
nids, and then called upon Mr. Arthur Lister, F.L.S., who read the
following note:—
On the Parasitism of Rotifers in Cysts on Vaucheria.
"On the 23rd of February, 1882, I gathered Vaucheria geminata, Vauch.,
var. racemosa, Hass., and V. aversa, Hass., growing together in full fruit
in a pond near Wanstead Church, Essex.
" On examination I noticed growing out from the stems of the plants,
and occasionally from the extremities, many clavate green capsules, from
five to ten times the breadth of the stem in length, often crowned with
from two to four horn-like processes, and almost invariably containing
one, but in a very few instances two, 'Wheel-Animalcules' (Rotifers),
which were observed feeding upon the chlorophyll-granules lining the
walls of their cage, picking off the granules with their much-extended and
pointed mouths, reminding one of the way in which earthworms feed
upon a dead leaf.
" In the older capsules, from which almost all the chlorophyll had
vanished, the animal exhibited very sluggish movements. It was nearly
globular in form, the anterior and posterior extremities slightly projecting;
a large dark granular spot (the liver?) occupied the central region, a
rotatory disc could be detected at the mouth, also two red eye-spots, a
ciliated alimentary canal, a gizzard of apparently simple structure, and a
contractile vesicle above the short bifid tail. The creature was distended
with eggs, and was surrounded by free eggs, often as many as fifty in
number, which completely filled the chamber.
" In many of the capsules a writhing movement was observed within
the egg; in others, some or all had hatched, and the young were actively
moving about their enclosure, or making their way along the dead stems
of the Vaucheria, with which the capsules had free communication. I
noticed two or three of these young ones crawling outside the plant,
but whether or not they had escaped from broken stems I could not
determine.