76 



THE BEHAVIOR OP' I.OVv'ER ORGANISMS. 



animal behavior in general. In the study here set forth observation 

 w^as directed primarily to the questions of how 

 certain Rotifera react under the stimulus of 

 the agencies which usually give rise to the so- 

 called tropisms — light, chemicals, heat, elec- 

 tricity, contact, etc. — and to these questions 

 the present account will be devoted. 



The species whose reactions were exam- 

 ined belong chiefly to the loricate group of 

 free-swimming Rotifera, and include a num- 

 ber of species of the Rattulidae, several species 

 of Cathypnadae, two or three species of Euch- 

 lanis, Plcesoma lenticulare^ Anurcea cochle- 

 aris, and Brachionus pala. These were 

 studied as opportunity offered. In most cases 

 the reactions of any one species were not 

 determined with relation to more than two 

 or three classes of stimuli. The behavior of 

 Anurcea cochlearis was examined most fully. 

 This species will be used as a type in describ- 

 ing the reactions. I have already given a 

 brief account of the general reaction type in 

 certain species of the Rattulidas in my mono- 

 graph of that group (Jennings, 1903). 



METHOD OF LOCOMOTION. 



The free-swimming Rotifera progress 



through the water in the same manner as the 



ciliate infusoria. The cilia in the Rotifera 



are limited to the anterior end, as they are 



in the peritrichous infusoria. It is interesting 



to note that the same device is adopted in the 



one group as in the other, to compensate for 



irregularities in the form of the body, etc., 



Fig. 25.* which might result in swerving from the 



straight course. This is by revolution on the long axis, causing the 



path to become a spiral with a straight axis. In the Infusoria the 



* Fig. 25. — Spiral path followed in ordinary swimming by Anurcea cochlearis 

 Gosse, showing different positions of body in different parts of the course; 

 a, dorsal surface; b, left side; c, ventral surface; rf, right side. The animal 

 revolves on its long axis over to the right., thus taking successively the positions 

 «, b, c, d, a, etc. The large arrow indicates the general direction of the course 

 followed; the smaller arrows show direction of progression in certain parts of 

 the course. 



