THE BEHAVIOR OF OTHER INFUSORIA 



"5 



Fig. 79. — Reaction of Oxytricha, ventral 

 view. 1-4, successive positions. 



distinguished, so that the direction of turning after stimulation can be 

 determined with the greatest ease. In many respects the Hypotricha 

 are among the most favorable objects to be found among unicellular 

 animals for studying behavior. 



Microthorax sulcatus usually creeps along the bottom, and reacts to 

 most stimuli by turning suddenly toward the convex ("dorsal") edge. 

 The turning may or may not be 

 preceded by a start backward. 



Colpidium colpoda (Fig. 31, 

 d) usually moves forward with 

 one side against the substratum, 

 following a curve with its oral 

 edge on the concave side of the 

 curve. When stimulated me- 

 chanically or chemically, it turns 

 toward the aboral side and con- 

 tinues its course (Fig. 80). 



In some cases the reaction to strong stimulation takes on special 

 features. For example, in Pleuronema chrysalis, in Halteria grandi- 

 nella, and in various Hypotricha, there are powerful bristle-like cirri, 



by means of which the animal 

 may leap suddenly backward 

 or to one side. These are 

 probably to be considered 

 strongly marked avoiding re- 

 actions, not differing in prin- 

 ciple from what we find in 

 Paramecium or Oxytricha. 

 Fig. 80. — Path of Colpidium. At 2 it is AH the species which usu- 



slightly stimulated; it thereupon turns toward the ally mOVe along On a SUrface 

 aboral side (3-4) and continues its curved course. , . ■ • r 1 



may at times swim freely 

 through the water. They then as a rule revolve on the long axis, both 

 when progressing and in the avoiding reaction. On the other hand, 

 almost all the species which characteristically swim freely through the 

 water do at times move along surfaces. They may then react to 

 stimuli in the same way as do the Hypotricha. Such forms as Bursaria 

 and Loxophyllum are transitional between the free swimming species 

 and those that creep along surfaces; they are found about as often in 

 one situation as in the other. 



In the Ciliata thus far considered the reaction method is evidently 

 that of the selection of certain environmental conditions through the 

 productions of varied movements. When its movement leads to stimu- 



