66 NATURAL HISTORY OF BRITISH FRESH-WATER LEECHES.
treated of in standard zoological text-books. It may be re
marked, in passing, that these systems are of the same general-
type met with in Annelids.
Leeches are hermaphrodite, and the canals carrying the
genital products open on the ventral surface of the body. The
male genital pore is anterior in position to the female genital.
pore, and the number of rings separating the two is a very
important character. It has been pointed out by Goddard
(18) that all the members of any genus, from whatever part of
the world they are taken, fall into two groups, one of which has
the genital pores separated by one ring, while in the other
group two rings intervene.
Habits and Life-History.—Harding gives the number of
species of British Leeches as fourteen. Of these three are marine
and the remainder live in fresh-water or in fairly damp places.
The true land-leeches belonging to the genus Haemadipsa are
not represented in Britain.
The fresh-water leeches are found in ponds and streams,
under the leaves of water plants, and under stones and logs.
They all travel by a looping movement with the alternate applica-
tion of the suckers to solid bodies. The members of the group
Arhynchobdellae are able to swim about by undulating their
bodies in an eel-like fashion, but this power is not possessed
by the Rhynchobdellae.
The eyes of leeches, although simple in structure, are capable
of recognising the varying intensity of light, Prof. Whitman
(45) observed that when a shadow was cast over a dish con-
taining a number of hungry Clepsines, they immediately raised
the anterior end of the body as if in search of prey. When a
turtle was placed in the dish they immediately fixed themselves
upon it. and began to feast. The attention of the Medicinal
Leech may be attracted by striking on the surface of the water
with a stick, or splashing the water. This is similar to what
occurs when cattle and horses go to drink. Ebrard (14), p. 92,.
states that when the leech gatherers agitate the water with
their feet, the leeches rise to the surface, remain there a moment,
and then swim towards the men. He says that they are not
guided by sight, but by the direction of the impulses given to 
the water. He confirmed this by pushing the water in a tank