152 Richard M. Fraps 



Assenmachcr (1) described testicular atrophy and failure to respond to 

 artificial illuniinalion in ducks bearing extensive lesions in the supraoptic 

 and paraventricular region of the anterior hypothalamus. These lesions 

 were hand placed, and possibly always damaged the paraventricular nucleus, 

 in which event there need be no incompatibility with the results described 

 by Ralph (50). Nor do Ralph's findings necessarily exclude participation 

 of the supraoptic region in the accelerated response which might be 

 expected under lengthened photoperiod. 



Considering the results of these several investigations insofar as they bear 

 on gonadotropic functions of the anterior pituitary, Ralph (49) suggested 

 that afferent neural stimuli and the effects of hormones "are in some manner 

 mediated, in large part or entirely, by neurosecretory cells of the hypo- 

 thalamus, particularly those of the paraventricular nucleus, and it is the 

 activities of these cells which are responsible for regulation of gonadotropin 

 release in the hen". This summary view of hypothalamic function and 

 indispensability in the hen is in accord with conclusions arrived at by others 

 (see (60)). 



While the central role of neurosecretory cells in regulation of pituitary 

 gonadotropin function seems thus to have been established, we should 

 emphasize again that we do not know the duration of the stimulus which 

 effects OIH release specifically. This may be brief, as was noted earlier. If 

 so, it is conceivable that the stimulus effecting "release" may act at the level 

 of the median eminence to cause or to permit an abrupt outpouring of 

 accumulated neurosecretory material into the portal vessels. In the male 

 white-crowned sparrow, Oksche et al. (46) state that the median eminence 

 can be regarded as a depot of neurosecretory material, exceeded only by 

 the neurohypophysis. They remark also on the reduced quantity of the 

 substance seen in the median eminence of birds on a 20-hr photoperiod 

 during the second half of the daily photoperiod and on its reaccumulation 

 during the dark period. It would obviously be of great interest to know 

 whether such a depletion of neurosecretory materials does or does not take 

 place in the hen in association with OIH release from the pituitary, not only 

 in the median eminence, but also in the paraventricular nucleus. Legait (40) 

 observed an association between reproductive condition of the hen and 

 apparent neurosecretory activity of cells of paraventricular and supraoptic 

 nuclei, but these observations were not related to presumed time of OIH 

 release. 



HYPOTHESES OF THE OVULATION CYCLE 



Several hypotheses have been proposed to account for lag, or for lag and 

 the period of lapse, in the hen's ovulation cycle (3, 15, 42-44). It is assumed 

 that external stimuli, and more particularly light, act through the central 

 nervous system to regulate, over neuroendocrine pathways, the output of 



