730 



REPRODUCTION AND MIGRATION IN BIRDS 



111 



encephalic 

 receptors 



hypothalamic 



neurosecretory 



nuclei 



axonic transmission 

 of "neurosecretory" 

 material 



"special zone" of 

 median eminence 



portal transport of 

 'neurosecretory" material 



1 



adenohypophysis 



circulatory transport of 

 gonadotropic hormone 



Fig. 4. A schematic repre- 

 sentation of the mechanism 

 of photoperiodic stimulation 

 of testicular growth. (Based 

 largely on the investigations 

 of Benoit and colleagues.) 



testes 



