284 Frederick Tilney, 



has shown no response as yet to juxtaposed evagination from the 

 mouth. 



Chick of 5 days and 20 hours. Embryo no. 227 (plate XV, fig. 24). 

 The marked change in this stage is the complete separation of Eathke's 

 Pocket [25] from the oral cavity [26\. The pouch itself, still retaining 

 its cavity, has become more expanded and its dorsal surface is juxta- 

 neural in position. A long slender stalk [19] extending from the 

 cephalic extremity of the pouch connects the latter with the mouth 

 cavity. As this stalk is about to enter the mouth a second small 

 diverticulum is observed, which represents the remnant of Seessel's 

 Pocket [31]. Near the cephalic pole of the body of the pituitary 

 anläge two sprouts are given off, one on either side, which in the 

 light of their further development may be considered the tuberai 

 processes [30]. The floor of the diencephalon [27] has formed a 

 ventral diverticulum which is in relation with the caudal extremity 

 of the pituitary anläge and denotes the inception of the infundibulum 

 and the infundibular process. 



Chick of 6 days and 22 hours. Embryo no. 463. In this stage 

 the buccal sac is still further separated from the floor of the third 

 ventricle. Its connection with the mouth is attained by means of a 

 long slender stalk at whose oral extremity appears the remnant of 

 Seessel's Pocket. The tuberai processes have assumed a more definite 

 juxta-neural position. The infundibular process has now become a 

 branched diverticulum from the floor of the diencephalon, while a 

 small ventral protrusion from this region marks the inception of the 

 saccular eminence. 



Chick of 8 days. Embryo no. 315. This embryo shows a marked 

 increase in growth of the infundibular process and eminentia saccu- 

 laris. It also illustrates the manner in which the tuberai processes 

 are assuming their intimate juxta-neural relations to the saccular 

 eminence. 



Chick of 10 days and 22 hours, no. H 75. At this period of de- 

 velopment the pituitary gland has lost all connection with the mouth 

 cavity, its stalk and the residuum of Seessel's Pocket having both dis- 

 appeared. While the dorsal surface of the body of the pituitary 



