THE LEEOHES OF JAPAN. 409 
should say that these Leeches are able to distinguish between 
a frog and a fish without being brought into contact with 
them. 
This Clepsine is a fish parasite, and would be a favorable 
object with which to test this question. 
I have made some experiments with one of our large pond 
Leeches (Macrobdella) for the purpose of ascertaining, if pos- 
sible, the function, or functions, subserved by the different 
sense-organs. I have not been able to settle the main question, 
but the results are perhaps worthy of brief notice. The ex- 
periments were as follows : 
1. The muddy bottom of a pool inhabited by these Leeches 
was shaken and stirred up by walking through it. This dis- 
turbance aroused the Leeches, and set them to swimming about 
in search of the intruder. I watched for any signs of method 
in their attempts to find me; and in various ways tried to find 
out if they were able to guide their course by a sense of sight, 
of smell, or of touch. The experiment was made in rubber- 
boots, on a bright sunny day; and, after starting the Leeches 
in the manner described, I remained quiet and observed the 
result. More than fifty Leeches made their appearance in the 
course of an hour. They swam about in all directions, the 
number coming towards me not exceeding those taking any 
other course. They sometimes halted, coming to rest on some 
plant, and then started up the moment the water was again 
disturbed. While on the move they generally kept at the 
surface, often throwing the head slightly above the surface; 
and when coming to rest they assumed an attitude, not of 
repose but of watchfulness, as if waiting for fresh evidence of 
my presence. I am not fully satisfied that their course was 
directed wholly at random, but I was unable to get any 
satisfactory evidence that they were able to orient themselves 
with reference to the place from which disturbing waves 
proceeded. Waves were made, by the hand or foot, to strike 
them from the side and from the rear; but they called forth 
no intelligent response, and only in comparatively few instances 
induced a change of course. The change of course in answer 
