740 REPRODUCTION AND MIGRATION IN BIRDS 



conditions, can be explained readily. These differences are usually 

 more striking in early-breeding resident species than in migratory 

 species. Although this scheme has a plausible basis in our existing 

 knowledge, it is, of course, essentially hypothetical and must be tested 

 experimentally. Any examination of this hypothetical scheme must 

 consider a possible difference between spring and fall in the ratio 

 and sequence of production of the tubule-stimulating gonadotropin 

 (follicle-stimulating hormone) and the gonadotropin (s) (Nalbandov, 

 Meyer, and McShan, 1951) which cause the formation of the cells of 

 Leydig and stimulate them to secrete. It is to be hoped that the 

 necessary experiments will be forthcoming in the near future. 



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Assenmacher, I., and J. Benoit. 1953a. Contribution a I'etude des relations 

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. 1953b. Repercussions de la section du tractus porto-tuberal hypophy- 

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. 1956. Nouvelles recherches sur les relations entre la neurosecretion 



hypothalamique, le system porte hypophysaire et I'activite gonadotrope de 



la prehypophyse. Compt. rend., 242, 2986-88. 

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 Benoit, J. 1934. Activation sexuelle obtenue chez le canard par I'eclairement 



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1935b. Role des yeux dans Taction stimulante de la lumiere sur le 



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71. 

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