HYPOPHYSIS OF PETROMYZON AND AMIA 



263 



Embryo represented 



0.1 "■'i 



Petromyzon planeri. Embryo twenty-two days old. 



Since the measurements are all to the same scale the units 

 are unimportant. 



The fact that the distance between the apex of the depression 

 and the notochord does not decrease, while that between the 

 apex and the extremity of the upper lip increases rapidly, 

 supports my contention that the hypophysis depression is not 

 an invagination but is brought about by the relative growth 



NO. 266 T 



