NATURAL HISTORY OF BRITISH FRESH-WATER LEECHES. 69
is satisfied that the cocoon is firmly fixed, it withdraws the
body in the following manner. A wave of dilation passes for-
ward along the body, enlarging the posterior orifice of the cocoon,
which is thereby detached at its hinder part. The fore part
of the body is then drawn backwards, but instead of simply
passing out of the sheath, it brings the two extremities of the
cocoon into contact, by a process of invagination. The body is
withdrawn and in less than a minute the cocoon assumes its
natural egg-like shape without the help of the leech. In the
case of Herpobdella the animal presses down the margins with
the aid of the anterior sucker and fixes the edges by means of a
secretion. This produces the oval, dome-shaped cocoon
characteristic of this species, in which the apertures through
which the body has passed may be seen in the form of two
dots—one near each end of the cocoon. Brumpt goes on to
say: At the moment when the cocoon is deposited the anterior
part of the body, contaminated with bacteria, infusoria and a
number of other impurities, is not brought into contact with
the contents of the cocoon. It would seem that a paradoxial
problem had been solved, viz., to pass through an albuminous
mass without touching it. The cocoon is deposited with due
regard to aseptic precautions.
All the members of the Sub-order Arhynchobdellae deposit
cocoons which receive no further attention from the animal.
The same statement, of course, applies to Piscicola geometra,
described above. A group of leeches forming the Family Glossosi-
phonidas carry the eggs on the under side of the body in some
cases, and in others the eggs, though deposited on foreign bodies,
are brooded over by their parents. The young when hatched
attach themselves to the body of the parent and are carried
about for some time. A primitive maternal instinct seems
to have been developed in some instances. A specimen of
Protoclepsis tessellata, taken by the writer, laid 36 eggs on the
side of a glass tank and brooded over them. When prodded
with a pen holder, the mother struck out viciously. Unfor-
tunately the eggs never hatched, but some months afterwards
three small specimens of the same species were placed in the
tank with the adult. Two of them immediately attached
themselves to the underside of "her" body. The third, which
was a little larger, refused to seek protection of a foster-parent.