THE DEVELOPMENT OF AN INSTINCT 279 



instinct on that day. For purposes of comparison we have 

 reproduced as a standard a curve of development of reaction 

 4, plotted from the average daily records of twenty-one chicks 

 (curve S, figure i). Curve I is based on similar records of four 

 animals whose practice in pecking was prevented, as above 

 described, up t© the beginning of their fourth day. The records 

 of group II are not presented on account mainly of their incom- 

 pleteness. Curve III shows the development of the instinct in 

 a group of six chicks, also beginning their practice on the fourth 

 day. In curve IV are represented averages for three chicks 

 which were released from darkness at the beginning of the fifth 

 day. There were six individuals in this group when the first 

 records were taken. Of six chicks originally in group V, five 

 died within three days after the first pecking records were 

 taken. Curve V represents the records of the one animal that 

 completed the tests. Practice was begun in this case on the 

 sixth day. For data see table i. 



One of the most interesting features of the results is the very 

 low initial records of all the chicks in which the action of the 

 instinct was delayed. Who would have predicted that the 

 greater maturation of groups I to V would not have enabled 

 them to begin at a higher grade of efficiency than that of the 

 standard group on the second day? As a matter of fact, all 

 the chicks in the above groups began their pecking as the merest 

 novices. Once we see the value for improvement of the first 

 attempts, the fact that these records are in every case lower 

 than the beginning records of the standard group may well be 

 explained on the ground that the chicks of the standard group 

 had twenty-four hours of freedom in the light prior to their 

 first tests, whereas the other chicks were tested immediately 

 upon being released from the dark-room. 



The next point that seems to be of rather exceptional interest 

 is the rapidity and amount of improvement during the first 

 two days of practice. Within this time the dark-room chicks 

 attained the level of accuracy normal to their age. Thence- 

 forward . the progress apparently assumed its natural course. 

 It seems probable that the peculiar change in the shape of the 

 standard curve at the beginning of the third day is not entirely 

 a matter of chance. The rest of the curves are of the same 

 general character, — a rapid advance with the first two days of 



