MOVEMENTS, ETC., OF FliElSH-WATEU PLANAIUANS. 513 



made the subject of such a study. The behaviour of typically 

 uusjaiiinetrical organisms, the Infusoria, has been analysed, 

 as has also that of some radially symmetrical animals, and in 

 both cases there is found to be a very close interrelation- 

 ship between the general form of the body and the reactions. 



To investigate, then, in a comprehensive way the activities 

 of a bilaterally sj'^mmetrical organism standing low in the 

 animal series was the purpose of this work. The most 

 general problem which presents itself is the establishment 

 of the animal's position in the objective psychogenetic series. 

 Are its activities relatively simple or are they complex ? Do 

 they fall under the same general type as those of the 

 Infusoria or those of the higher organisms, or do they occupy 

 an intermediate position ? Another general probleui of im- 

 portance is whether there is any marked correlation between 

 the behaviour and the form of the body, such as has been 

 found to obtain in so marked a degree in the case of the 

 Infusoria and the rotifers (vide Jennings, loc. cit.). We 

 have in the Hat-worm a symmetrical animal; are its reactions 

 of a s^'mmetrical type? Besides these broad fundamental 

 problems there are, of course, a large number of subsidiary 

 questions which readily suggest themselves in connection 

 Avith a work of this sort. These need not be specifically 

 mentioned here, but will be brought out in the course of 

 the paper. 



As to the scope of the work as actually done, the following 

 may be said: — The general ''natural history'' of the animal 

 was studied as completely as possible. All the normal move- 

 ments were studied in detail. The reactions to mechanical 

 stimuli; the food reactions and reactions to chemicals in 

 general; electrotaxis ; thigmotaxis; rheotaxis; the righting 

 reaction ; the reaction of cut and regenerating pieces ; and 

 hydrotaxis and the reactions during desiccation were investi- 

 gated. No work was done on the phototaxis or theruiotaxis. 

 A study of the phototaxis was omitted for two reasons; first 

 on account of the fact that during the progress of this in- 

 vestigation Parker and Burnett (: 00) reported their work on 



