ANIMAL BEHAVIOR. 287 



The contribution which I have to offer aims at no extensive 

 exposition of the subject, but rather to call attention to some 

 phenomena which I have observed, and to connect therewith 

 such interpretations and theoretical considerations as may come 

 within the sphere of general biology. 



In animal life there are many interesting modes of keeping 

 quiet, which are instinctive and adapted to special purposes. 

 It is a very general means of concealment and escape from 

 enemies. For illustration, we may take first the leeches, ani- 

 mals relatively low in the scale. One of the lower and least 

 active forms, occurring everywhere in ponds, lakes, and streams, 

 is known under the generic name Clepsine. There are many 

 species, varying from one-quarter inch to one inch or more in 

 length. They are found on their regular hosts, turtles, frogs, 

 fishes, molluscs, etc., or on the under side of stones, boards, 

 branches, or other submerged objects near the shore. One of 

 the larger species, found often in large numbers on turtles, will 

 be favorable for observation. 



BEHAVIOR OF CLEPSINE. 

 a. Deceptive Quiet. 



Place the animal in a shallow, flat-bottomed dish and leave it 

 for a few hours or a day, in order to give it time to get accus- 

 tomed to the place and come to rest on the bottom. Then, 

 taking the utmost care not to jar the dish or breathe upon the 

 surface of the water, look at the Clepsine through a low magni- 

 fying 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 experiment is properly carried out, it 

 will be seen that the respiratory undulations (if such move- 

 ments happen to be going on) suddenly cease and that the 

 animal slightly expands its body and hugs the glass. Wait 

 a few moments until the animal, recovering its normal compo- 

 sure, again resumes its respiratory movements. Then let the 

 needle descend through the water until the point rests on 

 the bottom of the dish at a little distance from the edge of 

 the body. Again the movements will cease and the animal 



