CONTROL OF ANNUAL GONADAL CYCLES 729 



ship between wavelength and testicular response as noted previously. 



It is obvious then, at least in domestic ducks, that both ocular and 

 encephalic receptors are involved in photostimulated testicular de- 

 velopment. It appears obvious also (Benoit and Assenmacher, 1953b, 

 1954a, 1955) that for equal intensities of light, the encephalic 

 receptors may be more sensitive. In view of the fact that in the intact 

 animal they would be subjected to lower intensities, it is not possible 

 at present to designate quantitatively the possible relative roles of the 

 two groups of receptors. 



Although a detailed knowledge of the tracts involved is lacking, it 

 is obvious that impulses from the ocular receptors, and presumably 

 also from the hypothalamic receptors, exert an effect on neurosecre- 

 tory cells of the hypothalamus. A series of experiments with domestic 

 ducks (Assenmacher and Benoit, 1953a,b, 1956; Benoit and Assen- 

 macher, 1954b; 1955) have led to the conclusion that a regulatory 

 material (identical with, or similar in behavior to, the Gomori-positive 

 neurosecretory material) formed by the cells of hypothalamic nuclei 

 passes down the axons of these cells into the median eminence, where 

 at least some of the material passes into the capillaries of the hypo- 

 thalamo-adenohypophysial portal system, which then transports it to 

 the adenohypophysis. In these experiments it was found that either 

 sectioning the hypothalamo-hypophysial tract above the "special zone" 

 (the zone of contact between the portal capillaries and the loops of 

 the neurosecretory axons), of the median eminence, or sectioning the 

 hypothalamo-adenohypophysial portal system (including insertion of 

 a hard disc to prevent reestablishment of circulation) eliminated the 

 testicular response to photostimulation and caused atrophic changes 

 in the cephalic lobe of the adenohypophysis. On the other hand, in 

 birds with the stalk sectioned below the "special zone," leaving the 

 portal circulation intact, both the photoperiodic testicular response 

 and the cephalic lobe were normal. Shirley and Nalbandov (1956) 

 found marked ovarian atrophy in the domestic fowl after section of 

 the stalk including complete severance of the portal circulation. 



Although it is obvious that the photoperiodic testicular response 

 involves neurosecretory cells of the hypothalamus, their axons, and 

 the hypothalamo-adenohypophysial portal system, it must not be 

 assumed that this simply involves an elevated production and trans- 



