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376 THE AMERICAN NATURALIST. [VOL XAXI 
the path of course becomes a spiral; it agrees exactly with the 
path of Paramecium, in that the aboral side always looks toward 
the outer side of the spiral. At times the animal swims some 
distance without revolving on its long axis; at such times the 
path is not a spiral. 
We will now proceed to a systematic examination of the 
changes in motion due to stimuli of different sorts and applied 
at different points on the animal’s body. 
A. Me hanrsi Stimuli. 
The method of study consisted in touching with a capillary 
glass rod, of less diameter than the animal’s body, different 
points on the surface of the animal, and noting the reactions 
caused. This procedure presents no difficulties. 
1. Stimulus at Anterior End. — If the animal is touched at 
the anterior end with the tip of the glass rod, it immediately 
contracts strongly, becoming short and thick, and the zones of 
cilia forming spirals surrounding the body, in the manner well 
known. (See the figure given by Bütschli in Tze Protozoa of 
Bronn's Klassen und Ordnungen des Thierretchs, Taf. LX VII, 
Fig. 2 6.) At the moment of contraction it darts backward a 
little. It then gradually extends, continuing to swim backward. 
As it swims backward it revolves on its long axis, in all cases 
observed, from right to left, in the same direction as when 
swimming forward. Next it begins to turn its anterior half to 
one side, usually at the same time beginning to swim forward. 
Like Paramecium, it always turns toward the aboral side of the 
anterior end. It usually revolves at the same time, so as to 
describe a very wide spiral, with the aboral side on the outside 
of the spiral, finally straightening out and swimming forward 
in the direction indicated by the position of the aboral side at 
the time it straightens. Briefly, the animal when stimulated 
at the anterior end contracts, backs off, turns to the aboral 
side, and swims forward on a path which lies at an angle 
to the path on which it was previously swimming. In the 
case of a very slight stimulus the contraction may be 
omitted, the rest of the reaction being given as usual, ex- 
