PHOTOPERIODISM IN FEMALE DOMESTIC FOWL 777 



Cycles 



In Fis. 1, successive ovipositions in a 3-member sequence appear 

 as Li, Lo, and L3. No egg is laid on the following day, and a new 

 sequence is initiated on the day thereafter with the oviposition Li'. 

 The sequence of ovipositions together with events between the ter- 

 minal oviposition of one sequence and the first oviposition of the next 



24 48 72 96(0) 24 



J > J I' J '.' 2 1 JT'' I !' _ 



"* "^ — y «i 'SM m 



Oi 02 03 or __02' 



[ ^^ ^°^ ■ L—JsL 



86 86 86 86 86 86 66 



Fig. L Time relationships in a 4-day cycle (n = 3). Lighted hours 

 6:00 A.M.-8:00 p.m.; hours of darkness, 8:00 p.m.-6:00 a.m., are set off 

 by the vertical stippled bands. 



constitutes the oviposition cycle. This is a cycle in a limited and 

 rigorous sense, i.e., the course of events returns to its proximate start- 

 ing point. The cycle as defined here includes only a single day on 

 which oviposition fails to occur. Cycle length is thus equal, in days, 

 to sequence length plus 1 , or to n + 1 • 



The ovulation cycle consists similarly of the sequence of ovulations, 

 Oi, O2, and O3 of Fig. 1 and events between O3 and Oi'. Preceding 

 the ovulation cycle is the OIH release cycle; onset of each release is 

 indicated by Ri, R2, and Rs in Fig. 1, and Ri' marks the beginning of 

 another cycle. A cycle at the nervous level precedes the cycle of OIH 

 releases; the effects of photoperiod are expressed in this neural com- 

 ponent of the mechanism of OIH release. 



Sequences and Lag. The difference in times of day at which suc- 

 cessive ovipositions take place has been defined as lag (Fraps, 1954). 

 The interval between successive ovipositions in any sequence is thus 

 24 -f /? hours, where h represents lag. In the 3-member sequence of 

 of Fig. 1, /2L2 and hhs represent lag in time of ovipositions L2 and L3 

 respectively. The "asynchronous rhythm in the time of egg laying" of 



