HYPOPHYSIS OF PETROMYZON AND AMIA 



287 



the distance between the hypophysis and the anterior extremity 

 of the notochord is much reduced. This may mean that the 

 tip of the notochord has grown forward, or that the hypophysis 

 itself has moved back. The tip of the notochord appears to 

 be stationary and to bear fairly constant relations to the limits 

 of the hind-brain, so that the movement must be sought for 



Text-fig. 29. 



Fb 



AdO.- 



llliL 



Imm 



Amia calva, 6 mm. long. Hyiwphysis completely separated 

 from its point of origin and wedged between the brain and 

 the dorsal wall of the gut. 



Text-fig. 30. 

 Fb 



Amia calva. The same as Text-fig. 29, higher magnification. 



in the hypophysis itself. Such movement could hardly be due 

 to active migration since the hypophysis is firmly held between 

 brain-floor and gut-roof, but is rather to be explained as the 

 passive result of the movement of the latter. This movement 

 may be due to the ' recoil ' resulting from the forward growth 

 of the anterior of the fore-brain as suggested by Eeighard and 

 Mast, or to shrinkage of the gut-roof in the region posterior to 

 the hypophysis, which would have the effect of drawing back 



