Leeches 33 



funnel with the wide opening outward. In the upper sloping face 

 a row of holes was bored and covered with wire mosquito screen. 

 Except for these openings and the slit-like entrance the box was quite 

 tight. In using the trap a bait of freshly killed frogs or more 

 frequently a duck bag filled with fresh blood was suspended inside 

 from the top in such a position that the blood dripped onto the 

 upper sloping side and trickled through the openings above the 

 entrance. The box was then weighted with stones and sunk to the 

 bottom in shallow water close to shore. 



The theory of operation of these traps is as follows. The blood 

 flows from the openings above the entrance and diffuses into the 

 surrounding water. Judging from the known habits of the blood- 

 suckers, any in the vicinity might be expected to be stimulated by the 

 scent or taste of the blood to follow the trail to its source where the 

 convergent sides of the funnel would direct them to the entrance 

 through which they would crawl into the interior. Once within the 

 box they would quickly find and attach themselves to the bait and 

 after satisfying their appetites would drop off and seek a dark shelter 

 as is their habit. This would be afforded by the lower chamber of 

 the trap where it was expected they would remain quiescent and 

 satisfied until the trap was examined on the following day. Even 

 should some of them become restless and crawl or swim about there 

 would be little chance of their finding the narrow opening by which 

 they entered, and the more direct openings for the diffusion of blood 

 are in the upper chamber and guarded by a screen. 



Three of these traps were made and set at favorable points chiefly 

 in the shallows at the southern end of the lake where the leeches 

 were most common. They were shifted about from time to time in 

 order that as many conditions as possible might be tested. They were 

 baited as often as fresh bait could be procured, that is, two or three 

 times a week for five weeks, and were always examined on the 

 following day. In some cases a bag of blood was dragged over the 

 bottom near the shore in both directions from the trap to establish 

 a better trail. Detailed records of each trap were kept but are not 

 worthy of publication. Suffice it to say that in no case was more 

 than a single leech found in any trap and more frequently there was 

 none. Freshly killed frogs proved a more attractive' bait than 

 slaughter-house blood. Concerning the ineffectiveness of the latter 

 see the remarks under the account of laboratory tests of baits. 



The second form of trap (figure 15) is a rectangular bag of duck, 

 the mouth of wliich is supported by a heavy wire frame. From the 

 mouth two duck flaps six inches wide project obliquely into the 

 interior and_ converge till they nearly meet, their free edges being 

 held in position close together by being stretched on a heavy wire rod. 

 The general effect of this trap is similar to the box trap, but the blood 

 bait diffused into the water through the sides generally as well as 

 through the narrow mouth. It was baited, weighted and sunk at 

 suitable points, usually being suspended above the bottom from an 

 anchored buoy by cords attached to the wire frame so that the open- 



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