CONTRIBUTIONS TO THE BIOLOGY OF THE GREAT LAKES. 
A REPORT OF WORK ON THE PROTOZOA OF LAKE ERIE, WITH ESPECIAL 
REFERENCE TO THE LAWS OF THEIR MOVEMENTS* 
By H. S. JENNINGS, 
Instructor in Zoology in Michigan University. 
The general plan of work outlined in the preceding paper for a study of the Pota- 
toria in their relations to the life conditions of the lake would apply equally, with 
some changes, to the Protozoa or to almost any other group of animals. In the study 
of the Protozoa it was decided to strike at once for the heart of the matter by begin- 
ning an investigation of the laws of their activities. A typical and very abundant 
Infusorian, Paramecium caudatum , was selected for special examination, and a study 
was made of the nature of its activities and the laws which govern them, in the hope 
that a full knowledge of such laws in the case of one Protozoan might furnish a key to 
an understanding of the activities of other members of the group, as well as, in time, 
to those of higher animals. The results of this work have already been published in 
detail elsewhere, so that a brief resume is all that will be presented here. 
The work was successful in determining the general mechanism of the reactions 
of Paramecium to changes in the external conditions, and in showing that the reactions 
are of the same essential nature in many other Protozoa. It was shown that the 
reactions of Paramecium are of extraordinary simplicity. As will be recalled by most 
biologists, Paramecium is a somewhat cigar-shaped animal, with one end narrow and 
blunt, the other broad but pointed. From the blunt end a groove passes obliquely 
along one side of the body to the middle, ending there in the mouth. The side on 
which the mouth and groove lie may be distinguished as the oral side; the opposite 
side (on which the contractile vacuoles lie) as the aboral side. The entire surface of 
the animal is covered with cilia, by means of which it moves. As it more usually moves 
in the direction of the narrower, blunter end, that may be called the anterior end, the 
other the posterior end. 
In what might be called the normal condition of affairs all of the cilia strike 
backward, so that the animal moves forward; at the same time it revolves on its long- 
axis. Now, when a change is produced in the environment of the Paramecium, such 
as by it striking against an obstruction or passing into water of different chemical 
content or different temperature, the normal activity is modified in one of two ways: 
1. If the Paramecium comes in contact with a solid body of a loose fibrous 
texture, its activity is decreased; the cilia on the surface of the body cease their 
4 The papers in this series are based on investigations of the U. S. Fish Commission under direc- 
tion of Prof. Jacob Reighard, of the University of Michigan. The following have already appeared: 
The Mechanism of the Motor Reactions of Paramecium. <(Am. Jour. Physiology, vol. n, pp. 
311-341. 
Laws of Chemotaxis in Paramecium. . <(Am. Jour. Physiology, vol. u, pp. 355-379. 
105 
