48 Herbert Eugene Walter 



Times 



1 Contracted, and turned aside 32 



2 Contracted, lifted up the anterior end, and turned aside 27 



3 Contracted, lifted up the anterior end and went straight forward 17 



4 Contracted momentarily and then went straight ahead 5 



5 Did not contract but turned aside 2 



6 Did not contract but lifted up the anterior end and turned aside 7 



7 Did not contract but lifted up the anterior end and went straight forward 9 



8 Did not contract but went straight ahead 1 



Total 100 



Animals which, like planarians, present a limited range of be- 

 havior are, therefore, more favorable subjects for experimentation 

 than higher forms whose structural complexity increases their possi- 

 ble responses, making in consequence the analysis of cause and 

 effect in their activities more difficult. It is evidently desirable, 

 then, to have as many different ways for measuring behavior as 

 possible, in order not to state these responses loosely from general 

 impressions but in quantitative terms. The principal criteria of 

 planarian reactions to light used in this study, follow: 



1 Rate of Locomotion. Since the entire range of possible rates 

 of locomotion depends upon the structure of the worm and is not 

 very great, slight differences become significant. 



2 Amount and Character of Turning, that is, whether persistent 

 or irregular, decided or vague, clockwise or contra-clockwise. 



3 Change of Course. A change in the character, but not neces- 

 sarily in the direction, of the course is referred to here. "Circus 

 movements," for example, would not be included under this head- 

 ing because the curving path in such cases, although constantly 

 changing in direction, does not change in character. Tangents to 

 a circle, however, as well as angular and abrupt deviations from 

 a straight line may properly be regarded as changes of course. 



4 Interval of Response. The apparent effect of light is not 

 immediate in all cases, therefore, the time elapsing between the 

 application of the stimulus and the response to it is a valuable 

 measure of reaction. 



5 Degree of Wandering. In a sense the degree of wandering 

 shown by a worm is a measure of its indifference to the stimuli 

 acting upon it. It must be noted, however, that apparent indif- 



