^^-^^] Gee: Behavior of Leeches 



221 



of Clepsine {Glossiphonia) Whitman (1898) says: "They prob- 

 ably recognize their right host by the aid of organs of taste; 

 at any rate, they are often able to distinguish their host from 

 closely allied species." Glossiphonia stagnalis assumes a very 

 characteristic feeding position, similar to that of the last stage 

 of the looping reaction. The posterior sucker is fixed close to 

 the place of attachment of the mouth, and rhythmical muscular 

 movements pass antero-posteriorly over the body. This sucking 

 action must serve to rupture the epidermal tissues of the earth- 

 worm, since this species of leech does not possess denticulate 

 jaws. The hold is scarcely loosed until the leech has completely 

 gorged its digestive tract. The outline of this stands out plainly 

 through the partially transparent cells of the body wall. When 

 in this condition of mechanical fullness the animal relea;3es its 

 hold on the unfortunate victim, and moving away soon comes to 

 rest in the society of its fellow-leeches, which perchance are 

 already undergoing the wholesome effects of a bloody meal. 



4. Sensitivity to Various Stimuli 



Whitman (1898) has pointed out from some of his experi- 

 ments the extreme sensitivity of Clepsine. He placed leeches of 

 this genus in a shallow, flat-bottomed dish and allowed them 

 time to become acclimated. "Then taking the utmo.st care not 

 to jar the dish or breathe upon the surface of the water, look 

 at Clepsine through a low magnifying lens and see what happens 

 when the surface of the water is touched with the point of a 

 needle held vertically above the animal's back. If the experi- 

 ment is properly carried out, it will be seen that the respiratory 

 undulations (if such movements happen to be going on) suddenly 

 cease and the animal slightly expands its body and hugs the glass. 

 Wait a few moments until the animal, recovering from its normal 

 composure, again resumes its respiratory movements. Then let 

 a needle descend through the water until the point rests on the 

 bottom of the di.sh at a little distance from the edge of the body. 

 Again the movements will cease and the animal will hug the 

 glass with its body somewhat expanded. Now push the needle 

 slowly along towards the leech and as the needle comes almost 



