32 BRISTOL. [Vol. XV. 



and explore. They are as likely to explore away from the food 

 as towards it. If, while swimming, any portion of the body 

 touches the food, a leech will often perceive it, stop short, and 

 feed on it. 



If a leech is feeding, any other leech that comes in contact 

 with it perceives instantly what the other is doing and rapidly 

 creeps along its body to partake of the meal. I have frequently 

 started up every individual in a bunch of a dozen or more, by 

 gently pushing a morsel to one which projected its head a little 

 beyond the others. The first motion of seizure would be enough 

 to set the whole bunch in commotion. If a bit of food be 

 gently placed on the back of an individual at rest, it will often 

 whirl rapidly about and seize it, though it remains indifferent 

 to another leech creeping over the same place. If, in a clear 

 aquarium containing some hungry Nephelis, the finger be rubbed 

 over the bottom and continued up the side out of the water, the 

 leeches as they creep along the bottom will perceive the scent 

 and follow the trail, even to some distance out of water. 



These experiments indicate the same general conditions of 

 perception as Professor Whitman has found in Macro bdella (lo). 



In the summer time Nephelis lives in the shallow waters of 

 the pond, but in winter it goes down to the deeper parts or into 

 the mud of the edges if there is a good food supply. I have 

 found them in midwinter in seven feet of water when the ice 

 was 25 cm. thick, and in another place in the mud near the 

 edge when the ice was 50 cm. thick, leaving only 8 or 10 cm. 

 of water over the mud. In both cases the individuals were as 

 active as in summer, and some of them laid eggs after being a 

 few weeks in the aquaria. These developed and produced nor- 

 mal individuals which in one instance gave me a supply of 

 small individuals very opportunely. 



Nervous System. 



When this work on the nervous system of Nephelis was 

 begun, the chief object in view was to determine the innerva- 

 tion of the somites as a means of elucidating the metamerism 

 of Nephelis. 



10 "The Leeches of Japan." Quar. Jourii. Micr. Soc, vol. xxvi, p. 317, 1886. 



