68 NATURAL HISTORY OF BRITISH FRESH-WATER LEECHES.
of reproduction. As stated above, they are hermaphrodite,
but self-fertilization does not take place. The spermatozoa
are enclosed in a case or spermatophore, the shape of which
depends upon the species. Generally speaking, they are lance-
shaped and are driven through the skin of another individual.
The precise spot at which they are introduced is immaterial,
but it is generally on the dorsal surface and in the region of the
clitellum. A portion of the spermatophore remains projecting
from the body for some time after impregnation. The sper-
matozoa enter the body cavity and gradually make their way
to the ovaries. Phagocytes are produced by special phagocytic
organs, and it has been suggested that the former consume
empty follicles and excess of spermatozoids which may remain
after the period of egg-producing is over. In some cases the
injection of the spermatozoa is brought about by the elasticity
of the walls of the spermatophore, in others the ejaculatory
canals furnish the necessary force. Impregnation and deposi-
tion of the cocoon has been studied in detail by E. Brumpt
(10). The descriptions given below are taken chiefly from his
paper.
From some observations made by the writer on specimens
of Herpobdella, about six days elapsed between impregnation
and the deposition of the first cocoon. Brumpt states that the
average period is two days in the case of H. atomaria. The
period is much longer in some other species. A specimen of
Protoclepsis tessellata, taken by the writer on May 6th, did
not lay eggs until the middle of June. The period in this case
must have exceeded five weeks.
In order to describe the process of cocoon laying, I cannot do
better than give a free translation of Brumpt's description of
what he observed in the case of Piscicola geometra. A suitable
spot having been chosen, the Piscicola fixes itself by the two
suckers and applies its body to the wall of the vessel. The
white cuticle formed by the. clitellum is gradually detached
from the skin and looks like a large annular blister. The animal
then fixes the band to the glass and, relaxing its anterior point
of support, rolls itself around on its axis, evidently endeavouring
to remove the band from the body. At intervals it takes a
rest, allowing the fore part of the body to hang limp, a position
which gives the animal an air of exhaustion. When the animal