30 BRISTOL. [Vol. XV. 



ous on a mud bottom as on a sand bottom. This was a matter 

 of surprise to me until I found the explanation. I noticed 

 that I invariably made the best collections on the shore that 

 looks towards the prevailing summer winds ; that is, the shore 

 towards which the surface current flows, bringing with it 

 crustaceans, dead fish, and various other food materials. The 

 windward shore is almost always barren of Nephelis, for the 

 water on that shore is the cool water of the deeper parts and 

 is poor in food for Nephelis. That this food supplying current 

 is the important factor in influencing the distribution of 

 Nephelis is beautifully demonstrated in the small fresh-water 

 ponds near Woods Holl. 



These ponds lie in basins scooped out by glacial action, and 

 many of them have no outlet. Some are nearly circular, 

 others are elliptical or long and narrow. The surrounding 

 hills are comparatively high, and the direction of the prevailing 

 wind over the pond is frequently determined by the trend of 

 the lower land or valley near the pond. This exposure to 

 wind varies in different ponds lying near together, and Nephelis 

 are always more abundant on the lee shore. In brooks they 

 are usually more abundant near the mouth of the stream, 

 whether it flows into another stream or into a pond. This is 

 explained in the same way. Food brought down by the brook 

 is more plentiful at that point than at any other. 



Habits, Food, etc. 



Nephelis, like Aulostoma, is non-parasitic and differs from 

 the parasitic leeches in many of its habits. It does not readily 

 leave the water like Hirudo or Macrobdella, and in confinement 

 it seldom attempts to leave the aquarium after the first twenty- 

 four hours, if there be plenty of food. It swims freely and 

 rapidly with the same undulating movement that Hirudo 

 employs. In creeping it never brings the anal sucker up to 

 the oral sucker as Clepsine, Hirudo, and Macrobdella, but 

 usually attaches it about halfway between the two in the out- 

 stretched body. In common with other leeches, Nephelis has 

 the habit of fixing itself by the anal sucker and then undulating 



