Ovulation in the Domestic Fowl 139 



FSH preparation could well be attributed to contamination with LH. On the 

 basis of these results, Fraps et al. (26) concluded that the luteinizing fraction 

 was "identical with the avian ovulation-inducing gonadotropin". 



It is of some interest in connection with the proposed unitary concept that 

 similar ratios of gonadotropic activity were found in the pituitaries of cocks, 

 non-laying hens and laying hens when the glands were assayed for FSH 

 content mainly (55) or for ovulation-inducing eflFect (13). 



Insofar as relationships between follicular maturation and release of 

 ovulation-inducing hormone (OIH) are in question, it is perhaps of little 

 importance whether we think in terms of LH or of the postulated gonado- 

 tropic complex. What is important is the timing of OIH release with reference 

 to follicular maturation and, to anticipate the final issue, whether or not the 

 timed release of OIH is under control of the central nervous system. 



Returning to Fig. 2, the relationships believed to exist between follicular 

 maturation, OIH release, and ovulation are represented schematically for the 

 4-day ovulation cycle described earlier. Onset of OIH release during the first 

 "day" of the cycle is indicated by Rj; OIH acts on the mature follicle, Q, 

 to effect the first ovulation, Oi, of the cycle. In similar fashion, OIH releases 

 associated with Rg and Rg induce ovulation of the Cg and Cg follicles. No 

 release of OIH occurs on the following day, but does so on the day thereafter, 

 Ri' initiating a succeeding cycle. 



As thus formulated, the onset of OIH release is assumed to take place at 

 an approximately constant interval before each corresponding ovulation of 

 the cycle. It follows that lag at Rg and Rg, indicated by hRg and hRg, are 

 the same as lag at Og and Og. And since all ovulations, whatever the length 

 of sequence, occur within restricted hours of the 24, the onset of correspond- 

 ing OIH releases must occur within similarly restricted, but earlier, hours of 

 the 24. Days of the cycle given in the topmost lines of Fig. 2 refer to this 

 aspect of the OIH release cycle, not to ovulation as such. Onset of OIH 

 release may occur within hours 0-8 or so of the cycle day, not during remain- 

 ing hours of the 24, set off by the horizontal bars near the top of Fig. 2. 

 The hours of the 24 during which onset of OIH release may occur have been 

 denoted the release or open period, the remaining hours the period of 

 lapse (17); these are indicated by p and q respectively between hours 72 and 

 96 (day 4) of the cycle. 



To result in ovulation, the presence of a mature or ovulable follicle 

 obviously must be posited at the time of each OIH release; it does not follow 

 that the presence of an ovulable follicle is closely associated with OIH 

 release. Once a cycle is initiated with OIH release for ovulation of the Ci 

 follicle, successive follicles of the sequence must mature within the interval 

 (24 hr + lag) separating successive releases of OIH. The fact that this is so 

 seems obvious in the observation that, at the time of a given OIH release 

 (e.g. Ri of Fig. 2), the follicle next due to ovulate remains completely 



