ESSEX REPTILES AND AMPHIBIANS. 151
happen if the animal is sickly, and I have had myself awful cases
of chameleons (and once a bat) destroyed in this way. The
greenbottle, so disgustingly common in London gardens
(Lucilia sp), will lay its eggs in the nostrils of a living tortoise,
but I have never seen this happen to a frog or a toad. One-eyed
toads, I am sure, are animals which have swallowed either blue-
bottles or greenbottles.
5.—THE FROG (Rana temporaria).
I recorded "one year" frogs on the 17th March, in 1917;
and, as with the toad, they seem to be constantly earlier than
the "two year old's." A collector who supplies the frogs used
in London hospitals and schools has often assured me that he
finds all three stages wintering together at the bottom of ponds.
These congregations are very great. In October, 1912, he took
1,400 frogs in two days from a drain at Uxbridge; and in Decem-
ber, 1918 he showed me part of a batch of 800 taken from a small
pond. These, by the. way, were crooning vigorously. I have
heard frogs, deep in the water, crooning as late in the year as
October at Theydon Bois, and it is not unusual to come across
lively individuals at all seasons when using a net in ponds. The
dealer I mention believes that when a pond is totally cleared
in midwinter, it will soon be occupied again. This means, of
course, that frogs are more active on mild winter nights than
most of us think.
The lake at Birch Hall accommodates many frogs, which spawn
always in colonies. In 1914, 15, 16, and 17 the egg masses were
scattered along a short stretch of bank on the western edge near
the boathouse. In the latter year the eggs were all laid together
in a single batch. During these years the increase in an area
of Lesser Reed-Mace (Typha minor) quite altered the nature
of the margin, which before was clay, thickly covered with
Fontinalis and Hypnum. The. change, apparently, caused the
frogs to migrate; for in 1918 the spawn was deposited in a
huge patch at the shallow western corner of the lake, a hundred
yards away from the previous station. They used the place
again in 1919, when much of the spawn was frozen black by the
hard weather of March and April.
During the six years that the lake was under observation,
I never saw frogs' eggs away from their circumscribed breeding