JELLYFISH. 83
The food of most of the Cyanea captured by me appeared to
be constituted almost entirely of Ctenophores (Cdippe or
Hormophora and Pleurobrachia).
This medusa is also much infested with Hypena.
Any net constructed for the capture of medusae should
be constructed of skrimp and sewed on to a ring of about 16
inches diameter; a three-jointed rod, very strong, and 11 feet
long, is also essential if one is "fishing" from a pier or bridge.
Aurelia in the Thames fairway is sometimes 18 inches across
and weighs some pounds. Chrysaora rarely exceeds 8 to 10
inches diameter and Cyanea but very rarely exceeeds in the
Thames 7 inches, frequently four or five only, but I have seen a
capillata at Haven Gore which was 10 inches across.
In my efforts to ascertain to what extent I was being con-
trolled by the very artificial conditions of my aquaria and jars,
I determined to carry out collateral experiments in the open,
as far as possible. The difficulties were immense, and in
summer, with myriads of holiday makers crossing the flats,
wholly impossible. My efforts had therefore to be confined to
the winter, including the terrible years 1928 and 1929, when the
flats were covered with ice. The conditions imposed were
stringent. The pool had to be deep and away from enquiring
spirits and safe from bait diggers. It had also to be close to a
channel or passage ; if on a bank the eddy soon filled my pools
up.
I overcame the bait-diggers by using a well-dug hole which
they had already searched vigorously and enlarging it to about
15ft. by 5 ft. x 2 ft., choosing the spots (where such a hole existed)
at a place where the tide first seeped across the levels. Since
these flats are roughly two miles across and seven miles long
it was necesary to have marks which could be found in fogs;
for Hydra Tuba at strobilation time must be visited every fort-
night at the latest, every week if possible, and the marks must
not be understood by the public. My pools were one-third of
a mile away sometimes, so bricks, bottles, sticks, old boots,
rubber tyres, etc., were laid out and their bearings recorded.
In 1928 so bitter was the cold that I was unable to lift the
shells to examine their polyps after putting my hands in the pool
or to untie them and place them in my glass cells for examination.
The Hydra Tuba were allowed to attach themselves to bivalve