EXPLANATION OF FIGURES 1-7, PLATES 1-5. 



All figures were drawn under a camera lucida. 



Fig. I. A sagittal section tlirough the head of a 7 mm. embryo, to show 

 the beginning of the paraphysis and hypophysis. Objective Yz inch; ocular 

 2 inch. 



Figs. 2, 2a. Sagittal sections of the anterior region of a 10 mm. embryo. 

 In Fig. 2 the section passes through the median plane of the paraphysis, but 

 slightly laterad to the median region of the hypophysis. In Fig. 2a the section 

 cuts the hypophysis medially, and the paraphysis to one side of the median 

 plane. Objective 2 inch; ocular i inch. 



Fig. 3. A sagittal section of an embryo somewhat older than the one 

 represented in Figs. 2 and 2a. The hypophysis is cut medially, while the 

 paraphysis is cut somewhat to one side of its median plane so that its con- 

 nection with the fore-brain is not shown. Objective 2 inch; ocular i inch. 



Fig. 4. A sagittal section of the anterior region of an embryo of about 

 13 mm. length. The paraphysis is cut sagittally, while the hypophysis is 

 cut through its lateral edge. Objective 2 inch; ocular 2 inch. 



Fig. 4a. A parasagittal section through the dorsal part of the head of the 

 same embryo represented in the preceding figure. The paraphysis is seen 

 as a distinct vesicle lying between the fore-brain and the superficial ectoderm. 

 The forward growth of the velum into one of the lateral ventricles is also 

 shown. Objective 2 inch; ocular 2 inch. 



Fig. 4b. A sagittal section through the hypophysal region of an embryo of 

 the same stage as the one shown in Figs. 4 and' 4a. Objective % inch; 

 ocular I inch. 



Fig. 4c. A horizontal section through the hypophysal region of an embryo of 

 about the same age as the ones shown in Figs. 4, 4a, and 4b. The approxi- 

 mate plane of this section is indicated by the broken line in Fig. 4b. Ob- 

 jective Yz inch; ocular i inch. 



Fig. 5. A sagittal section of a much older embryo than the ones shown 

 in Figs. 4 to 4c. The paraphysis is cut almost exactly medially, while the 

 hypophysis is cut laterad to its median plane. Objective 2 inch; ocular 

 2 inch. 



Fig. 5a. A sagittal section of the paraphysal region of the same embryo 

 shown in Fig. 5. Objective Yo inch; ocular 2 inch. 



Fig. sb. A horizontal section through the paraphysal region of an embryo 

 of the stage represented by Figs. 5 and Sa. The approximate plane of the 

 section is indicated by the broken line a-b, in Fig. 5. Objective 2 inch; 

 ocular 2 inch. 



Fig. 5c. A sagittal section through the hypophysal region of the same 

 embryo shown in Figs. 5 and 5a. Objective Y3 inch; ocular 2 inch. 



Fig. 6. A sagittal section through the paraphysal region of a 7 cm. embrj'O. 

 Objective 2 inch; ocular 2 inch. 



