MOVRMKNTS, ETC., OF FRKSH-WATER FLANARTANS. 511 



b. lleactions to Chemical Stimuli — Cliemotaxis 



1. Reactions to Localised Chemical Stimuli 



a. Methods 

 j8. Results 



2. General Summary 



3. Unlocalised Action of Chemicals 



ITT. Thiffmotaxis and tlie Riirhtinj^ Reaction 

 a. Thip;mot.axis 

 h. The Rigiiting Reaction 



The Mechanism of tlie Reaction 



c. Summary 

 TV. Electrotaxis 



a. Methods 

 h. Results 



c. Meciianism of the Reactions 



d. Summary 



V. Reaction to Desiccation . 

 VI. Rheotaxis 

 G. Genekal Sommaky ANn Discussion of I^esults 



H. IjIST of IjITERATURE 



PAGE 



643 

 643 

 643 

 646 

 657 

 669 

 670 

 670 

 673 

 676 

 684 

 685 

 685 

 685 

 690 

 695 

 695 

 697 

 698 

 710 



A. Inteoduction. 



The present study has for its purpose the analysis of the 

 behaviour of the common fresh-Avater planarian into its com- 

 ponent factors. It is well known that, aside from the 

 researches of a few investigators on a small number of forms, 

 we have little detailed knowledge of the behaviour of lower 

 organisms. It is coining to be realised, too, that knowledge 

 of what an animal does is just as important in the general 

 study of life phenomena as a knowledge of how it is con- 

 structed, or how it develops. But it must be admitted that 

 until quite recent times the study of the activities of living- 

 things was a much neglected field in biology. The 

 publication of the ' Origin of Species ' gave the biological 

 pendulum a swing towards the study of phylogeny, from 

 which it is only just beginning to return. 



As a consequence of this concentration of interest on other 

 subjects, we possess an accurate and full knowledge of tlu; 



