454 



WILLIAM A. LOCY AND OLOF LARSELL 













Fig. 1 Cross section through pharynx and lung pouches of a chick embryo 

 incubated 51 to 52 hours. 



P'ig. 2 Similar section of a slightly older eniljr^vo (52 to 53 liours) showing the 

 well defined lung pouches. Figures 1 and 2 drawn by Gilbert H. S. Rech. 



Fig. 3 Two consecutive sections through the pharyngo-tracheal groove of 

 the same embryo. These sections are respectively 120 and 12S microns in front 

 of the one sketched in figure 2. 



Fig. 4 Sections through the same region of an ciiilnyo inculialcd .").") to 5fi 

 hours. 



