INSTINCTS AND HABITS IN CHICKS 21 



Other hand, the development of no. 8 on Dec. 12 was far behind 

 that of any chick in the above group of five on the same date. 



It looks very much as if (i) the development of the instinct 

 was retarded by disuse, and (2) the retardation was quickly 

 overcome with use. Several attempts to repeat these dark-box 

 tests with other chicks failed. On these later occasions the plan 

 was conceived of placing the dark-box inside the incubator just 

 before the expiration of the period of incubation, depositing 

 therein a few of the eggs, and allowing the prospective chicks 

 to hatch and remain in the dark enclosure till needed. For 

 some unforeseen reason the chicks did not appear. 



We turn now to a more thorough investigation of the " con- 

 genital definiteness " of the pecking reaction, with a view to 

 a quantitative determination of its course of development. 



c. The natural development of the pecking reaction, with a 

 collateral study of the effects of social influence. 1. Sources of 

 error. — In addition to what has already been said of the method 

 of taking records, the important sources of error might be men- 

 tioned. Investigators have noted the fact that the chick, if 

 it misses the grain at all, usually comes within a hair's breadth 

 of it. Hence, when the animal is working rapidly, it is sometimes 

 difficult to determine whether the bill hits the grain or not. In 

 the work herewith reported, a chick was credited with reaction 

 2 if there was any doubt between i and 2. In other words a 

 I was recorded only when the miss was positively observed. 

 The fact that more missing reactions seem to be recorded among 

 the later results may be due rather to modification of the ex- 

 perimenter than to variation in the groups of chicks. I feel 

 quite confident that I became a more efficient observer of the 

 missing reactions as the work progressed. 



Again, there are times when reactions 2 and 3 may be easily 

 confounded. A grain seized simultaneously with the strike may 

 almost immediately fly from the bill — like a cherry pit squeezed 

 between the fingers. This reaction, properly 3, may be confused 

 with the reaction where the grain is driven from its position by 

 the mere impact of the bill. Still, as one becomes familiar with 

 such cases, the difficulty of distinguishing them almost wholly 

 vanishes. 



Occasionally fewer than the regular number of reactions in 

 the daily series are reported for a given date. In such cases 



