756 REPRODUCTION AND MIGRATION IN BIRDS 



of rest; but the significant and similar response of group E shows 

 that no rest was necessary beyond the amount preceding lighting, 

 which was a two-week term of incubation. Group E was not deemed 

 large enough to divide for a pretreatment check, so the indices for 

 this group before treatment are unknown, opening to question the ab- 

 solute amount of increase after treatment. Otherwise the evidence in- 

 dicates that the length of the rest period is not an important factor 

 in the possible refractoriness of bobwhite hens. 



The response of group A4, the nonlaying adults, is of interest 

 because of its smaller increase than any of the other adult groups. 

 Assuming some tissue exhaustion or systemic depletion in the post 

 ovulatory groups, we might have expected group A4 to have re- 

 sponded with a superior development of latent resources. There is 

 no apparent explanation for the mediocre performance. One can 

 only hypothesize that the receptivity of aging reproductive tissues to 

 stimulation is conditioned by previous functional periods. 



Although the evidence indicates that postbreeding bobwhite hens, 

 regardless of the length of the postovulatory period, are not abso- 

 lutely refractory to light, a relative refractoriness of the adult hens is 

 suggested by comparisons with the performance of juveniles. The 

 5-month juveniles of group B gave a much greater response than 

 either the adults or the younger juveniles of group C. The experiment 

 with juveniles was repeated with similar results, 6-month juveniles 

 giving a greater response than adults or 3 ^/^ -month juveniles. Con- 

 sidering the superior juvenile response, one is reminded that fall court- 

 ship display among wild galliform birds is well known. Good pre- 

 sumptive evidence that such displays are based upon sexual precocity 

 is found in the reports of fall spermatogenesis in juvenile pheasants 

 (Hiatt and Fisher, 1947; Kirkpatrick and Andrews, 1944). Since 

 off-season gonadal activity of pheasants is characteristic of juve- 

 niles, it might be reasoned that hitherto undeveloped tissues of 

 juvenile quail hens are more light-sensitive than regressed tissues of 

 older hens. Although old bobwhite hens are not completely refractory, 

 their slower hypertrophy of reproductive tissues perhaps indicates 

 ovarian fatigue rather than a relative pituitary refractoriness. The 

 positive ovarian and oviduct responses of the postlaying adult is good 



