BRAIN OF THE AMERICAN ALLIGATOR 1 3 



The number of lobes or branches of the hypophysis has increased 

 considerably, and, under the low magnification used in the present 

 figure, they appear as a collection of irregular, granular masses, sep- 

 arated by narrow lines of connective tissue. Higher magnification 

 shows these masses to be composed of small, densely stained cells 

 resembling lymphoid tissue. 



The infundibular pit, ht'., does not show such intimate connection 

 with the cells of the hypophysis as was noted in the preceding stage. 

 It is, however, more distinctly separated from the infundibulum 

 proper by a lateral narrowing of its mouth, so that, in sections on 

 either side of the one represented in figure 6a, the pit is seen as a 

 separate, circular vesicle, distinct from the infundibular wall and 

 lying among the lobes of the hypophysis. 



No sign whatever of the pharyngeal sac is to be seen in this 

 embryo. 



Figure 7 represents the hypophysis of the 13-cm. embryo de- 

 scribed in connection with the paraphysis. The hypophysal stalk, 

 h. s., is here reduced to a slightly curved stump in connection with 

 the main body of the hypophysis ; its connection with the mouth is 

 completely lost. 



The body of the hypophysis still shows a narrow, slit-like lumen, 

 I., on the side below the infundibular pit, in'. 



The mass of lobules making up the hypophysis is more compact, 

 in this median region, than in the preceding stage, so that the con- 

 nective tissue septa are almost invisible, and the lobules seem to 

 have fused together to form larger lobes. The appearance of the 

 hypophysis under higher magnification is not different from what 

 was seen in the preceding stage. 



The infundibular pit, in\, has, in this figure, about the same ap- 

 pearance as in figure 6a, but, in sections cut laterad to the present 

 one, the pit is found to have a branched lobe on each side. Each 

 of these lobes is seen in parasagittal sections as two circular, thick- 

 walled vesicles lying among the lobules of the hypophysis, entirely 

 distinct from the ventral wall of the infundibulum proper. 



Summary 



The paraphysis in the alligator has long been mistaken for the 

 epiphysis, the latter structure being entirely absent. 



The paraphysis is first seen in embryos of 7 mm. length, as a 

 wide evagination of the roof of the fore-brain, just cephalad to a 

 transverse fold, the velum. This evagination early becomes partially 

 constricted ofif from the brain and foriTis a rounded, hollow mass 

 connected with the diencephalon by a wide stalk. As growth pro- 



