274 



RAYMOND PEARL 



broodiness the records of hen No. 251, as shown in Fig. 3, may be 

 examined. 



In all essential particulars this record is very much like that 

 of hen No. 75 given in Fig. 1. Here the first onset of broodiness 

 was on April 8. After 8 days laying began again; 14 eggs were 

 laid; the second attack of broodiness began May 1. After 10 

 days laying was once more resumed and again 14 eggs were 

 laid before the brooding instinct made its appearance. Laying 

 began after 9 days and this time 72 eggs were laid. The next 

 period of brooding occupied 9 days (i.e., between laying dates). 

 This case is noteworthy for the evenness of the " clutches " and 

 of the intervening brooding period. 



Figure 3. Egg record of bird No. 251. 



RECURRENCE OF BROODING INSTINCT WITH DIFFERENT DEGREES 

 OF INTENSITY IN THE SAME HEN 



From an examination of any large collection of egg record 

 statistics in which broodiness is recorded it will be found that 

 there occur not infrequently individuals in which the instinct to 

 brood is manifested with different degrees of severity at different 

 times, indicating a similar variability in its underlying physio- 

 logical basis. 



An example of this phenomenon is shown in Fig. 4, which gives 

 the record from November 1 to July 1 of bird No. 4. 



Here it will be seen that the first period of broodiness began on 

 March 16 and the hen did not again lay until April 2. After 

 laying 4 eggs, she again became broody on April 8, but the period 

 did not last as long as the one before since she was released on 

 April 18 and was laying on the 19th. She did not again become 

 broody until June 14 and this period lasted only 4 days. The 

 bird was released from confinement on the 18th of June and laid 



