ORGANIC MOVEMENTS IT 



concede a very limited validity to the views recently 

 brought into the field, and maintain the old " taxis "- 

 theory. 



The new doctrine of " taxis," and at the same time 

 quite a new theory of the elements of animal movements 

 in general, is due to Herbert Jennings. 1 Jennings made 

 his important discoveries by studying not only the final 

 result of any directed agent acting upon the organism, but 

 also the moving individual itself in the very ad of moving. 

 This very act of moving, especially in the case of Protozoa, 

 was proved to be anything but a single and unbroken act 

 of turning. " Taxis " thus became a mere resultant of the 

 most various single motor acts, and, with the sole excep- 

 tion of galvanotaxis, ceased to be a proper name for the 

 process. 



I shall be only following the historical line of events, if 

 I now try first to give a short sketch of Jennings' solution 

 of the problem of taxis, and then begin the real systematics 

 of animal motions. 



The Resolution of " Taxis ''' 



The infusorium Paramecium is " positively chemotactic ' 

 to a weak solution of acetic acid, that is to say, a number of 

 these Protista living in a dish that contains a drop of such 

 a solution in any part of the water after a certain time will 

 be found to be all in a certain region around this drop, 

 which, of course, is slowly diffusing into the surrounding 

 water. The old theory would say in this case, that the 



1 Compare his work, Behaviour of Lower Organisms (New York, 1906), 

 where the full literature is to be found. 



