INSTINCTS AND HABITS IN CHICKS 53 



errors." On the basis of these results with black-blue there 



seemed to have been developed one habit of response to optical 



stimuli that would serve both for a measurement of the rate of 



modification in the chick and, when used along with another 



method yet to be discovered, as a test of the interrelation of 



modifications. 



TABLE 13 



Black-Blue Reactions 



Chicks nos. 16 to 20. Hatched 2/5, '08. 



No. 16 No. 17 No. 18 No. 19 No. 20 Av. 

 Sex,F. Sex, F. Sex, F. Sex, F. Sex, M. No. 



of 



Series Date RWRWRWRWRW errors 



A Feb. 17 55 55 37 46 55 5.6 



1 " 18 3 7 3 7 19 6 4 4 6 6.6 



2 " 19 3 7 3 7 5 5 5 5 6 4 5.6 



3 " 20 6 4 7 3 2 8 3 7 6 4 5.2 



4 " 21 9 1 82 82 64 82 2.2 



5 " 22 7 3 10 5 5 6 4 8 2 2.8 



6 " 24 9 1 9 1 9 1 6 4 9 1 1.6 



7 " 25 6 4 10 7 3 10 10 1.4 



8 " 26 10 10 9 1 10 10 0.2 



9 " 27 10 10 10 10 10 0. 



10 "28 9 1 9 1 0.4 



11 " 29 10 10 0. 



12 Mar. 1 10 10 0. 



13 " 2 10 10 0. 



The persistence of habits and their effects, as well as the 

 bearing of the results upon the problem of color vision, will be 

 discussed separately in a later section of the paper. For the 

 present, interest is confined to certain aspects of the process 

 of modification, and the question as to whether the reaction 

 of the chick is determined by the quality as well as the intensity 

 of the color stimulus is not a matter of special concern. The 

 term color is used simply to denote a certain stimulus, with no 

 implication that the chick's reactions are affected by variations 

 in wave-length of the ether vibrations. 



Let us turn now to the search for a second method of measur- 

 ing modification. 



B. Form 



To test the animals' responses to forms, black cards, cut as 

 previous cards, were used in the regular card-holders of the appar- 

 atus. The cards bore two-dimensional forms above the openings 

 through which a chick had to pass on its way out of the appar- 



