PHOTOPERIODISM IN FEMALE DOMESTIC FOWL 779 



= 2) is greater than at any other place in the sequence, decreasing 

 gradually with increasing sequence length until n = 7 or 8 and re- 

 maining thereafter fairly constant. In sequences of five or more mem- 

 bers, lag in the terminal place or two is somewhat greater than at the 

 immediately preceding place or places. Minimal values of lag gradu- 

 ally decrease with increasing sequence length, and approach or equal 

 zero in the longer sequences (« = 10 to 14). The number of ovula- 

 tions in a sequence may therefore be increased indefinitely with no 

 increase in total lag or other characteristics as long as daily lag 

 fluctuates around zero. For the sequences of Fig. 2, total lag is in fact 

 practically constant (ca. 7 hr) for n = 7 or greater. 



The Period of Lapse. As we have seen, total lag measures those 

 hours of the twenty-four over which ovulation may occur. Since the 

 onset of OIH release is assumed to occur for all members of a se- 

 quence at a constant interval (ca. 7 to 8 hr) before ovulation, lag 

 relationships are the same with respect to these events and are so 

 represented in Fig. 1. The open periods between the heavy bars near 

 the top of Fig. 1 represent the hours of the twenty-four during which 

 onset of OIH release may occur, the bars the hours during which on- 

 set of release never occurs. On the last day of the cycle (hr 72 to 96) 

 onset of OIH release fails to occur either during the period of usual 

 release, p, or during the following hours, q, the period of lapse. 



The courses by which follicles become mature are indicated sche- 

 matically by the curves Mi, M2, Ms, and M/ of Fig. 1. The essential 

 point is that each follicle in continuing cycles attains maturity (or be- 

 comes ovulable) in a constant relationship to the preceding ovulation. 

 The first or Ci' follicle of any sequence therefore matures (curve M/) 

 long before it is actually ovulated. This is demonstrated by the fact 

 that the injection of luteinizing preparations at about the time Q of 

 Fig. 1 readily induces ovulation (Neher and Fraps, 1950). Moreover, 

 progesterone, which apparently acts through the nervous component 

 of the OIH release mechanism (Fraps, 1955a) also induces ovulation 

 after injection at about the time Q. These and other observations 

 (Fraps, 1955a,b) lead to the conclusion that not only does the ovary 

 carry an ovulable follicle at about the time Q, but also that the pitui- 

 tary is capable of full response at or about this time. It follows that 



