84 THE BEHAVIOR OF I.OWEK ORGANISMS. 



while progression and revolution on the long axis had largely ceased. 

 After this circling had continued for some time, the swerving toward 

 the dorsal side apparently continually increasing, it was found that the 

 anterior end was directed away from the source of light; /. <?., the 

 direction of swimming had been reversed, and the animal was moving 

 away from the light. 



It is obviously very difficult to be entirely certain of all that has hap- 

 pened during this period of extensive circling, as a matter of direct 

 observation. But the evidence seems to show clearly that the essential 

 point in changing the course is the swerving toward the dorsal side. 

 The following facts all point to this conclusion : (i) In the individuals 

 which turn at once it is possible to be entirely certain that the turning 

 is toward the dorsal side. (2) In the individuals which are circling it 

 is entirely clear that the swerving toward the dorsal side is greatly in- 

 creased, and there is no evidence of turning in other directions. The 

 only difficulty is that one cannot follow every evolution and be certain 

 that nothing else has occurred. (3) Analysis of this same reaction 

 when given in response to other stimuli, where the conditions are 

 more favorable for observation, shows that it does consist of an in- 

 creased swerving toward the dorsal side, with a decrease, or an entire 

 stoppage fora time, of the forward motion. There is, then, no reason 

 to think that the reaction contains other factors when performed under 

 the influence of light. The reaction is indeed clearly the same as that 

 described for Euglena on p. 53, and illustrated in Fig. 21 ; a similar 

 analysis could be given for the reaction of Anurrea. 



It may be considered certain, therefore, that in Anurcea cochlea r is 

 the reaction to light is similar to the reaction to other stimuli, and that 

 the orientation is brought about by a turning toward the dorsal side. 

 The reaction is, therefore, not due to the direct effect of the light on the 

 motor organs ; the direction of turning is determined not by external 

 factors, but by internal factors. The reaction to light in the rotifer, 

 like that in the infusorian, takes place by the method of " trial and 



error." 



REACTION TO THE ELECTRIC CURRENT. 



A considerable number of different species of the rotifera were sub- 

 jected to the continuous electric current without the production of any 

 characteristic reaction. A current was used which could be graded in 

 strength from practically zero to one that was destructive, but no reac- 

 tion comparable to that found in the ciliate infusoria was produced. 

 On making or breaking the current the animals frequently contracted 

 quickly, and if the current was very strong, the head was completely 

 retracted and the animal sank to the bottom. But there was no orien- 

 tation and the animals did not swim toward either electrode. These 



