STRUCTURE OF FOUR-DAY CHICKS 151 



in its associations. (See Chapter XI and Figures 30 and 32.) 

 The portion of the ccelom which gives rise to the embryonic 

 body cavities is first marked off by the series of folds which 



al plat 



A 

 B 

 C 



dorsal mesoderm 



intermediate mesoderm 

 lateral mesoderm 



intermediate mesoderm 



intra-embryonic coelom 

 lateral body fold 



splanchnopleure 



primitive gut 



somatopleure 

 I J splanchnopleure 



mesonephric duct and tubule 

 _^ (from intermediate mesoderm) 

 fj^T lateral amniotic fold 



rr ^Ov. intra-embryonic coe 



:mbryonic coelom 

 extra-embryonic coelo 



liver in 



ventra 



mesentery 



ght and left 

 :oelom confluent 



FIG. 54. Schematic diagrams of cross sections at various stages to show the 

 establishment of the coelom and mesenteries. For explanation see text. 



separate the body of the embryo from the yolk (Fig. 54, C, D) . 

 As the closure of the ventral body wall progresses (Fig. 54, 

 E, F) the embryonic ccelom becomes completely separated from 



