THE ECTODERM AND ITS DERIVATIVES 



165 



will combine with the approximated and pigmented cells of the in- 

 grown hypophysis to form the pituitary gland of the adult. The in- 

 fundibulum cells give rise to the posterior part of the pituitary gland 

 and retain a hollow infundibular stalk connection with the brain. The 

 hypophysis becomes the anterior part of the pituitary gland. During 

 metamorphosis the individual lobes of the pituitary gland differ, both 

 in gross morphology and in finer structure. The lateral and inter- 

 mediate lobes show poor vascularization, a simple cellular structure, 



Diocoel 



Infundibulum 

 Mesenchyme 



Hypophysis 



Eye / Hypophy 



Infundibular sac 



Pharynx 



Notochord 



Infundibular sac Optic chiasma 



Development of the pituitary gland of the frog. (A) Relationship of the 

 hypophysis to the infundibulum as seen in a cross section through the 5 mm. 

 frog tadpole. (B) Same as "A" but enlarged to show the pigmented hypophyseal 

 cells as distinct from the gut endoderm. (C) The approximation of the hypophy- 

 sis and infundibulum as seen in a cross section through the 11 mm. stage. 

 (D) Sagittal section of the 1 1 mm. stage to show the relation of the hypophysis 

 and infundibulum to other parts of the brain and pharynx. 



