14
THE ESSEX NATURALIST.
of head blunt with a pair of very blunt tentacles. The eyes are placed
wide apart, and a slight constriction is to be seen behind them. The mouth
lies about two-thirds of the body length from the front margin, and im-
mediately behind the mouth, in the mature individual, a pale streak indi-
cates the position of the sexual organs. The sides of the body are almost
parallel over the greater part of its length. Posterior to the mouth the
body margins are frilled. Lobe formula of intestine 16-19, 2 (10-15),
16-19.
Habits. Occurs in ponds and in running streams under
stones and decayed leaves. It can withstand brackish water
and has been found in the Baltic Sea.
Bohmig (3) regards the species as a winter layer but Stein-
mann and Bresslau (36) state that it may come to maturity at
any time of the year. The writer has found sexually mature
individuals in March, April and August. Probably cocoons are
produced throughout the year in Britain. The cocoons are
dark brown, 2 to 3 m.m. in diameter, and contain from 5 to 42
embryos. The incubation period ranges from two to six weeks.
Transverse fission has not been observed in this species; its
power of replacing lost parts is slight.
Distribution:—
Britain. Epping Forest, Chigwell Row, R. Stort; East
London Waterworks, Tottenham; Regent's Park; Totteridge;
Staines; Rickmansworth; Elstree Reservoirs. (H.W.)
Ireland, France, Germany, Switzerland, Italy, Sweden, Russia.
At present D. lacteum is the only milk-white species of plan-
arian known in England. It is possible that some of the follow-
ing milk-white planarians may be found, viz.:—Planaria vitta,
with eyes, and Dendrocoelum infernale and Planaria cavatica,
without eyes.
Dendrocoelum infernale Steinmann.
The species is very similar to D. lacteum, but it is about half the
length and has no eyes. The uterine duct has an enlargement just
before opening into the atrium. The uterine duct of D. lacteum
(Fig. 1. ut.d.) is narrow throughout its course. Intestinal lobe-formula
15-18, 2 (12-15), 15-18.
It lives in streams both above and underground. It has not yet
been found in Britain, but has been recorded from Germany and
Switzerland.
Planaria cavatica Fries.
Synonym. Dendrocoelum cavaticum Enslin.
Milk-white, without eyes, and with two pointed tentacles. Frontal