94 Herbert Eugene Walter 



Finally, it may be recalled that in a preceding section data were 

 given (Table X, p. 68) to show that there is more response to light 

 while worms are upside down on the surface-film than when they 

 are in contact with the bottom of the aquarium, a difference 

 probably referable in large measure to the different thigmotactic 

 relations in the two cases. 



Goniotaxis. Goniotaxis is a term introduced by Pearl ('03, p. 

 561) to define a particular kind of thigmotactic response in which 

 the "different parts of the body are brought into such positions 

 that they form unusual angles with each other," as when a plana- 

 rian occupies the angle formed between a side and the bottom of 

 an aquarium. 



There is no doubt that the peculiar movements resulting from 

 the goniotactic stimulus directly modify the phototaxis of the 

 worm. Once in the angle of an aquarium a planaria'n becomes 

 increasingly indifferent to light. In one series of records, show- 

 ing how a considerable number of planarians came to rest, it was 

 found that the majority came to rest in an "angle" and that out 

 of this number 78 per cent failed to orient to the light. The stim- 

 ulus of the "angle" was greater apparently than the stimulus of 

 light. 



Furthermore, it is to be noticed that goniotaxis is always more 

 effective if the worm is in a lowered rather than in a heightened 

 physiological state, for whenever a planarian is freshly intro- 

 duced into an aquarium and is in an aroused condition on 

 account of the mechanical stimulation necessarily given it in 

 transference, it will pass over angles and crevices with total 

 indifference, all the while responding plainly to light. As soon 

 as it has become fatigued, however, if its path chances to cross 

 an angle or crevice it exhibits goniotaxis at once by slowing down 

 and remaining in the new situation, as if caught in a trap, with 

 complete disregard of the continued action of directive light. 



Chernotaxis. Pearl has made an extensive study of this phase 

 of planarian behavior and suggests that the well-known planarian 

 habit of collecting in groups may be explained on the supposition 

 that a resting planarian is surrounded by a halo of chemical ema- 



