THE BROODING INSTINCT IN THE DOMESTIC FOWL 273 



20. On the tenth day following laying was again resumed and 

 13 eggs were laid before broodiness again appeared on May 16. 

 On the ninth day following laying was resumed and 9 eggs were 

 laid before the appearance of the last recorded period of broodi- 

 ness beginning June 4. In this record the regular periodicity 

 in the recurrence of the brooding instinct, particularly as measured 

 by the number of eggs laid in the intervening ' clutches," is 

 striking. It will further be noted that in no case is the duration 

 of the " broody " period, as measured by the number of days 

 intervening between the laying of the last egg in one " clutch ' 

 and the first egg in the next, even approximately as great as the 

 normal period of incubation of the hen's egg, 21 days. The 

 treatment by confinement aborts the brooding instinct. An- 

 other point worthy of note is that the date of release, which indi- 



Figure 2. Egg record of bird No. 7o. 



cates the disappearance of visible symptoms of broodiness, in 

 each case precedes the date of beginning of the next " clutch ' 

 by some days. 



Another record of the same general type as the last, but in- 

 volving some different features is shown in Fig. 2. 



This record shows the occurrence of 5 periods of broodiness 

 with intervening " clutches " of 13, 10, 10 and 8 eggs. The 

 first period of broodiness occurred in the height of the breeding 

 season (April 9) and the instinct was evidently asserting itself 

 at this time with slight intensity. This is indicated by the fact 

 that only 4 days intervened between incarceration and release, 

 and that even then an egg was laid on the day of release. In the 

 later periods of broodiness the instinct apparently became progress- 

 ively more intense. 



As a final illustration of the typical cyclical appearance of 



