Ovulation in the Domestic Fowl 143 



of the pituitary preparation. This view is borne out by the decreasing order 

 of yolk weights in the lengthier successions of induced ovulations. Mean 

 weights of the second normally ovulated and the succeeding four yolks for 

 the 13 hens in which ovulation was induced 4 times or more were 17.4, 16.8, 

 16.2, 15.5 and 14.3 g. The mean difference between first and last members of 

 the series, 3.1 g, suggests that the secretion of FSH (or of the gonadotropic 

 complex) did not keep pace with the enforced demand for follicles capable of 

 maturation and subsequent ovulation. 



In any event, the level of pituitary response elicited repeatedly by pro- 

 gesterone at or near onset of the period of lapse lends no support to the view 

 that the normal ovulation sequence is terminated by pituitary inadequacy, 

 the period of lapse representing, as it were, a period of recovery (44). On the 

 contrary, onset of the period of lapse seems to indicate the abrupt intervention 

 of conditions which prevent response of an entirely competent anterior 

 pituitary to stimuli which otherwise are closely associated with the presence 

 of a mature follicle. And perhaps the resumption of ovulation, at a definite 

 hour of the 24 under a given photoperiod, constitutes equally cogent evidence 

 for a similarly abrupt termination of the conditions which impose the period 

 of lapse. If the relationship between mature follicle and pituitary response 

 seen during the course of the ovulation sequence depends upon a nervous 

 relay, so to speak, this relay appears not to respond, during the period of 

 lapse, to the usual stimuli associated with follicular maturation. OIH release 

 therefore fails to occur for lack of nervous activation of the pituitary, not 

 because of any defect in pituitary function. Evidence for this view will now 

 be considered. 



NERVOUS CONTROL OF OIH RELEASE 

 Basically, the anatomical and functional relationships between the hypo- 

 thalamus and the pituitary appear to be much the same in birds and in 

 mammals. The absence of direct nervous connections between hypothalamus 

 and pars distalis and the existence of a well-developed portal system (30) is 

 firmly established in birds (29, 67). In birds, the neurohypophysis is separated 

 from the adenohypophysis by a connective tissue septum, thus eliminating, as 

 Harris (31,32) has emphasized, any possibility of vascular control of the 

 anterior pituitary by the neurohypophysis. In his comprehensive monograph 

 on the avian pituitary, Wingstrand (67) described the tracts from the hypo- 

 thalamus to the neurohypophysis and along their course, a special region of 

 the median eminence in the ventral wall of the infundibulum, notable for its 

 content of neurosecretory material. From this region the pituitary portal 

 vessels pass to the anterior pituitary. Wingstrand, as did Green and Harris 

 earlier (30), concluded that hypothalamic control of the anterior pituitary 

 was effected by transport of some neurohumor from this region of the median 

 eminence to the secretory cells of the pituitary. 



