360 WILLIAM L. DOLLEY, JR. 



occurred. The insects generally moved in a peculiar, jerky 

 manner. The tendency to diverge from the direct path toward 

 the side of the uncovered eye was overcome by a series of short, 

 quick turns in the opposite direction, which kept them headed 

 toward the light." Mast ('11, p. 222) found that the toad, Bufo 

 americanus, with the lens removed from one eye, hops or walks 

 toward. a source of light, usually deflecting slightly toward the 

 injured eye. Some individuals, however orient nearly, if not 

 quite, as accurately after the operation as before. Thus, it is 

 evident that there are numerous exceptions to the idea that the 

 destruction of one eye is followed by circus movements. 



Moreover, it has been found that some animals which make 

 circus movements modify their behavior after having had a cer- 

 tain amount of experience, and move directly toward the light. 

 Holmes ('05), in a detailed description of the behavior of one 

 specimen of Ranatra with the right eye blackened, says that in 

 the first ten trials before an electric light, it made many circus 

 movements, and showed a ''marked tendency to turn to the 

 left." In the next four trials it turned directly toward the 

 source of light and in the succeeding ten trials it reached the 

 light by a nearly straight path. After an interval of fifty min- 

 utes, eleven more trials were made, ''and it had not forgotten 

 in the meantime how to reach the hght by the most direct means," 

 for it went to the light in everj^ case in a nearly straight course. 

 The author also states that other specimens of Ranatra and 

 Notonecta showed this same modification. Brundin- ('13, pp. 

 334-352) observed similar reactions in the amphipods, Orchestia 

 traskiana and Orchestia pugettensis, except that being negative 

 the animals turned toward the blackened eye. Mast tested on 

 two successive days a toad with one eye destroyed. He says 

 ('11, p. 222): "The following day this toad was again exposed: 

 it now went toward the source of light even more nearly directly 

 than on the preceding day." Thus, it is clear that the reactions 

 of at least some of these mutilated organisms may become modi- 

 fied as the result of repeated trials. 



This is apparently not true of some animals. Radl cut out 

 one eye of Hydrophilus, and states that, though it lived for 



