76 NATURAL HISTORY OF BRITISH FRESH-WATER LEECHES.
species of fresh-water fishes, and may remain on its host for
some days. It is fairly common in trout fisheries.
The cocoons are deposited on water plants, and each cocoon
contains one egg. According to Brightwell (9) the cocoons
are laid within 24 hours of copulation and the young are hatched
30 days after deposition of cocoon.
Distribution.—So far this species has not been found in Essex,
but it probably occurs.
Britain:—R. Thames, Bourne End (Blair) ; R. Wensum.
(Brightwell, 9) ; Eckington Canal (Evans, 15).
Ireland :—N. Ireland; R. Dodder, Co. Dublin (Scharff, 39).
Foreign :—Widely distributed in Europe.
Protoclepsis tessellata, O.F.M. (Clepsine tesselata). The
Chequered Leech. Plate VI., Fig. 2.
Description.—Body flattened, translucent. Large specimens have a.
brownish tinge, smaller ones are greyish and sprinkled with fine black
dots. When extended the body tapers slightly towards the anterior
end, but when contracted it is ovoid in outline. Length of adult about
25mm. The body has on its dorsal surface six well marked longitudinal
rows of greenish grey dots, while smaller dots are distributed irregularly.
The head has four pairs of eyes which are placed in two parallel rows.
Complete somite consists of three rings. The genital openings are
separated by four rings.
Habits.—Small specimens taken by the writer were very
active, but a very large one measuring 30 mm. long and 13 mm.
across when contracted and 55 mm. long when stretched was
very sluggish in its habits. It is found on weeds and under
stones. It drags the body along without raising it from the
ground, and is.unable to swim. Accounts of the egg-laying
habits of this species differ considerably. The large specimen
mentioned above deposited in June 36 eggs in 3 cocoons on
the bottom of the tank and then brooded over them. The
young when hatched attach themselves to the parents' body
(ante p. 69). Houghton and 0. F. Muller state the number of
young as 200 and 300 respectively, but it does not necessarily
follow that all the young attached to the body of an adult are
offspring of that individual.7 This species is parasitic upon
ducks and other water-birds. Examples have been taken from
wigeon, teal, long-tailed duck and domestic duck, the favourite
7 Mr. Blair furnishes me with the following note. "A specimen of this species laid 250 eggs
in three cocoons and hatched them all, but had to reject 100 as there was not room for them
to attach themselves to the parent. They hatched about 20 days after deposition."