MOVEMI'JNTS, KTC, Ob' FBE8H-\VATER I'LANAKIANS. 515 



recently by Wliittmm ('09). The aim in the present work 

 has been to get as extensive and detailed a knowledge as 

 possible of the behaviour of the organism by direct observa- 

 tion before resorting to experiments. 



At this point I wish to acknowledge my indebtedness to 

 the officials of the laboratory in which this work has been 

 done. To Professor H. S. Jennings, under whose general 

 oversight this investigation has been prosecuted, I wish to 

 extend my heartfelt thanks for his uniform kindness in 

 freely giving advice, suggestion, and kindly criticism of im- 

 measurable value. Any adequate expression of my iudebted- 

 ness to him is impossible. I further wish to express my 

 thanks to Professor Jacob Reighard for the numerous 

 facilities which I have enjoyed during my stay in his 

 laboratory, and for his kindly interest, which has made work 

 thei'e a pleasure. Finally, I desire to acknowledge my in- 

 debtedness to Professor F. C. Newcombe, of the Botanical 

 Department of the University of Michigan, for many 

 valuable suggestions and advice. 



B. Resume op LrrERATURE. 



But little has been done on the physiology of the move- 

 ments or on the psychology of the Turbellaria, and, as in 

 the case of most of the literature dealing with these subjects, 

 what has been done has been in comparatively recent years. 

 Investigators of the old " natural-history " school which 

 flourished before the time when Darwin's work changed the 

 course of zoology seem not to have given much attention to 

 planarians, while the later systematists and morphologists 

 for the most part carefully avoided any reference to the 

 activities of the forms which they studied. 



I. Morphological and Systematic. 



Among the papers devoted primarily to the systenuitic or 

 morphological treatment of the group, there are occasional 

 references to jioints in the behaviour of the oi-ganisms which 



