487 



The Tenth Day Stage. 

 From the beginning of the ninth day of incubation to the end of 

 the tenth day there is a steady growth of the various air-sacs and 

 of the recurrent bronchi. It is not necessary to follow in detail the 

 various steps between the two stages, since a description of the 

 conditions found in the later stage will sufficiently indicate the changes 

 through which the various structures have passed. 



Fig. 4. 



Fig. 5. 



Fig. 4. Latero-posterior view of right lung of late ninth day of incubation. 

 Shows recurrent bronchi {r.br.l and 2) of the abdominal air-sac (ab.) and (r.br.) of 

 the posterior intermediate air-sac, (p.i,). eel, first ectobronchus ; ec.6, sixth ecto- 

 bronchus; en.l, ventral and lateral branches of first entobronchus ; lat.l, first latero- 

 bronchus; lat.3^ third laterobronchus ; pr., prepronchial air-sac. Camera. X 31. 



Fig. 5. Lateral view of left lung of same specimen as shown in fig. 4. 

 Illustrates the five air-sacs and the primordia of the recurrent bronchi of the four 

 air-sacs possessing them in the adult, ab., abdominal air-sac; a.i., anterior inter- 

 mediate air-sac; br., bronchus; eel, first ectobronchus; ec.6, sixth ectobronchus; 

 en.l, first entobronchus; lat.l, first laterobronchus; lat.3, third laterobronchus; 

 pr.i., posterior intermediate air-sac; pr., prebronchial air-sac; r.br., recurrent bronchi; 

 S.l, mesial moiety of sub-bronchial air-sac; S.8, lateral moiety of sub-bronchial air- 

 sac. Air injected. Camera sketch. X 31. 



