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. Jt 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 Hczmadipsa 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 
Arhynchobdellse 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 
