aJOVEMENTS, ETC., UF FUESU-WATEU I'LANAlilANiS. 629 



time, since the stiuiulus is a rather slruug' one, the reaction 

 is a very precise ouO; and the subsequent movement carries 

 the animal directly io the food (Fig. 28, 7). This heluiviour 

 is typical for this sort of stimulation, but may vary in its 

 component phases, depeudiug- on the relative strengtli of the 

 stimulus — the distance from the food when first stimulated. 



N B 



Fig. 28. — Diagram showiiij; llic rcaclioiis of Plaiiaiia l,u food (A) 

 from which juices liavc l)i:cii diirusiiii^ into t ho walcr for some time. 

 B, B, B, represent the ell'ectivc marj^in of the (liH'usiDii area of the 

 food A. 1, 2, 3, i, 5, 6, and 7 are successive positions talvcn by 

 the organism. 



Thus eithei" two or as many as four positive reactions niay be 

 necessary to bring the animal to the food. This shows 

 clearly that with reference to chemical stimuli, the precision 

 of localisation of the positive reaction decreases as the in- 

 tensity of the stimulus iliiuinishes. Indeed, I have observed 

 what is L'viileutly nu unlocalised positive reaction, although 



