Ovulation in the Domestic Fowl 



153 



pituitary gonadotropin (whether FSH mainly, or the gonadotropic complex) 

 responsible for follicular growth and development. The frequency with 

 which follicles become available for the ovulatory process determines the 

 quantitative aspects of the cycle, viz., sequence length («), cycle length 

 {n+\) and ovulation frequency nj{n^ 1). 



The hypothesis of the cycle proper proposed several years ago (15) was 

 essentially a statement of possible relationships between diurnally varying 

 thresholds of response in a neural component of the OIH release mechanism 

 and excitation hormone (progestagen?) concentrations associated with 



Fig. 5. Diagrammatic representation of possible relationships between diurnal rhythmicity 

 in thresholds of response in a neural component of the OIH release mechanism (the curve 

 through El, Eg ... Eg and E/) and excitation hormone concentrations associated with 

 the follicles Cj, Ca . . . Cg and C/ in a 7-day cycle (n = 6). Zero hour corresponds to about 

 10.00 p.m. in hens under lights from 6.00 a.m. through 8.00 p.m. Based on Praps (15). 



follicular maturation. These relationships are shown for a 7-day cycle 

 {n = 6) in Fig. 5. Thresholds of response (the inverse of sensitivity) are 

 described by the curve passing through Ej, Eg... Eg and E^'. Excitation 

 hormone concentrations associated with successive follicles of the sequence, 

 assumed to increase by substantially the same course with respect to the 

 preceding OIH release (or ovulation), are represented by Q, Cg-.-Cg and 

 Ci'. The first excitation, Ej, takes place on day 1 of the cycle at zero hour in 

 the figure (e.g. 10.00 p.m.), initiating the release of OIH which causes 

 ovulation of the C^ follicle. The second excitation, E,, occurs on day 2, some 

 several hours later than did Ei on day 1 , the third somewhat later on day 3, 

 and so on through Eg, which takes place about 8 hr later on day 6 than did 

 El on day 1 and completes the sequence. In this scheme, it is to be observed 

 that each excitation hormone curve beyond the second (Cg) is displaced, in 

 time of day, by the extent of lag associated with the previous excitation. 

 If this is true also of the Ci' curve, excitation cannot occur on day 7 because 

 of the relatively high nervous thresholds existing at the time of day at which 

 usually effective concentrations are attained. The period of lapse (hours 8-16) 



