The Pituitary Stalk and Ovulation 59 



inhibitory influence on the secretory activity of the optic glands. Lesions in 

 the reflex arc thus allow a release effect on the optic glands, the secretory 

 product of which in turn stimulates the gonads. They compare this suggested 

 mechanism with that in insects in which, after the last moult, the corpus 

 allatum becomes a source of gonadotropic hormone under the control of an 

 inhibitory center in the supraesophageal ganghon and an opposing excitatory 

 center in the subesophageal ganglion. 



(ii) The Hypothalamus and Follicular Ripening following Anestrus 



The physiological factors responsible for regulating FSH secretion at the 

 beginning of the breeding season have received little attention. It is well known 

 that various environmental factors, such as conditions of hghting, are of 

 major importance in determining the onset of reproductive activity following 

 a period of sexual quiescence. Rowan (78) was the first to demonstrate that 

 artificial illumination during the hours of darkness in winter causes enlarge- 

 ment of the gonads and sperm production in the junco finch. These findings 

 were extended to mammals by Baker and Ranson (field mouse, 2) and 

 Bissonnette (ferret, 7). Other mammals whose reproductive rhythm has 

 been found sensitive to changes in light exposure include the rat, hedgehog, 

 cat, mink, goat and sheep. 



The ferret shows a well-marked breeding season from March to July or 

 August and in the estrous state exhibits a prodigious vulval swelling. On 

 account of these facts it has been used in experimental work to analyze the 

 light-estrus reflex. The following facts have been established: 



{a) Extra illumination with light of wave lengths 6500-3650 A (red- 

 near ultra-violet) accelerates the onset of estrus in winter (68). 



{b) The acceleration of estrus may be correlated with the intensity of the 

 extra illumination (67). 



(<?) Long periods of light alternating with short periods of darkness are 

 more effective than continuous illumination (42). 



{d) Hypophysectomized ferrets do not respond to extra illumination (55). 



(e) Section of the optic nerves or blinding by other means (8, 16, 79) frees 

 the onset of estrus from photic influence. 



It thus seems clear that the influence of light is mediated through the retina 

 and optic nerves to stimulate the release of FSH from the adenohypophysis. 

 The anatomical pathway intervening between the optic nerve fibers and 

 anterior pituitary cells is not clear. Data adduced by Clark, McKeown and 

 Zuckerman (16) and Jefferson (58) indicated that the pathway does not 

 involve the optic tracts in the region of the lateral geniculate body. In order 

 to see whether the central nervous pathway involved the pituitary stalk, 

 Donovan and Harris (18) cut the stalk in a series of female ferrets. They found 

 that animals in which regeneration of the blood vessels of the stalk (the 

 hypophysial portal vessels) had been prevented by placement of a waxed 



