144 RiC HARD M. FRAPS 



Experimental evidence, based largely on mediation of the effects of light 

 to the gonads, strongly supports the conclusions of Wingstrand (67) and 

 Green (29). From a series of experiments on the drake, the results of which 

 were considered in two general papers, Bcnoit and Assenmacher (5, 6) con- 

 clude that lengthened photoperiod is no longer capable of inducing the usual 

 gonadotropic response of the anterior pituitary deprived of blood from the 

 specialized region of the median eminence. In two recent papers Assenmacher 

 (1) and Benoit and Assenmacher (7) have emphasized again the dependence 

 of gonadotropic function on the integrity of neurosecretory regions in the 

 hypothalamus, of the hypothalamico-hypophysial tract to the special zone 

 of the median eminence, and of the anterior portal vessels forming the final 

 link with the anterior lobe. 



Hypothalamic-pituitary relationships have been investigated recently in 

 the male white-crowned sparrow, with special reference to neuroendocrine 

 functions in relation to photoperiod and gonadal response (46). The observa- 

 tions described by Oksche et al. are in accord with those of earlier 

 workers. 



In the regularly ovulating hen, Shirley and Nalbandov (61) reported 

 complete interruption of the portal vessels to result permanently in "a condi- 

 tion indistinguishable from hypophysectomy as far as the ovary and the sex 

 hormone-dependent structures are concerned". Neurohypophysectomy, on 

 the other hand, had no such effect and, following an adequate recovery 

 period, ovulation proceeded at the same rate as in unoperated controls 

 (62). 



As was noted earlier, these and other investigations have been concerned 

 mainly with seasonal or long-term gonadal responses, mostly to light, and 

 therefore with control of continuing secretion of pituitary gonadotropins. 

 The problem posed by OIH release may, at first sight, appear to be different 

 in some respects. The release of OIH is believed to be episodic, and to occur 

 in response to a specific stimulus of follicular or ovarian origin. It is at least 

 conceivable that such a stimulus, of "internal origin", might act directly on 

 the pituitary to cause the release of OIH. However, there is now good evidence 

 that this is not the case: whatever the stimulus for OIH release, it appears 

 to act initially at a neural level, thence over neuroendocrine pathways to the 

 anterior pituitary gland. This is not to say that the ovarian hormones may 

 not influence the anterior pituitary gland directly, but only that this appears 

 not to be true of OIH release. 



Photoperiod and the Period of Lapse 



We have called attention earlier to the highly significant circumstance that, 

 during most or all of the period of lapse, the ovary carries an ovulable follicle 

 and the pituitary is responsive to progesterone. What seems to be lacking is 

 some definitive connection between follicle and pituitary, a connection 



