No. I.] THE METAMERISM OF NEPHELIS. 31 



its body as in swimming. In repose it commonly seeks shelter 

 under a stone, a leaf, a clump of weeds, or in the upper layer 

 of mud or sand at the bottom, exposing only the anterior third 

 of the body. It rests in this position for comparatively long 

 periods and seems, at times, to be sleeping, or at least so slug- 

 gish as to require considerable stimulating before it responds. 

 Sometimes it rests curled up in a spiral with its head in the 

 center and attached by its anal sucker. When undisturbed 

 and active it creeps in search of food and stopping now and 

 then it attaches itself by the anal sucker and explores an arc 

 of the circle of which its body is the radius. The head sways 

 from right to left, up and down, while the body is extended 

 gradually to full length ; then the body is shortened and moved 

 through a small angle and the first process is repeated. 



When hungry, either at rest or creeping in search of food, 

 Nephelis is quick to perceive its presence ; but while swim- 

 ming it seems to be less attracted, although it may swim nearly 

 in contact with the foodstuff. My experiments were made on 

 leeches in aquaria, purposely left without food for some days. 

 Leeches fresh from the pond gave practically the same results 

 as leeches that had been kept in confinement for long periods. 

 When the water is about 3 cm. deep an individual at rest on the 

 bottom will perceive a portion of food let down gently over- 

 head almost as soon as it touches the surface ; after a short 

 interval, fifteen or twenty seconds, the leeches lying from 4 to 

 6 cm. away will give evidence of perception and they will set 

 out to find it. If at another time, when the leeches are bunched 

 together in a mass, the food be placed about 10 cm. away, a 

 minute or a minute and a half may elapse before one shows 

 any sign of awakening and starting in search of the food. 

 Others follow more or less rapidly at intervals. Under these 

 conditions there seems to be some evidence of a sense of 

 direction, but it is vague, if not mere chance. Some, not 

 always the first ones, will start off in the proper direction ; 

 others will stray afar ; some will come within i cm. of the 

 food and pass on without noticing it ; others will start to swim 

 briskly in irregular paths as if to trace the scent, and when 

 near the food will suddenly settle down, fix the anal sucker, 



