io6 



EARLY EMBRYOLOGY OF THE CHICK 



B 



neural fold 



ectoderm of head 



somite 



intermediate mesoderm 



somatic mesoderm 

 coelom 



splanchnic mesoderm 

 tf* — entoderm 

 avity of somite 



epithelial layer of somite 



core of somite 



pronephric tubule 

 (intermediate mesoderm) 



somatic mesoderm 



splanchnic mesoderm 

 entoderm 



epithelial layer of somite 



cavity of somite 

 core of somite 

 migrating cells 



posterior cardinal vein 

 mesonephric duct 

 mesonephric tubule 

 coelom 

 dorsal aorta 



dermatome 

 — sclerotome 



myocoele 



posterior cardinal vein 



mesonephric duct 



mesonephric tubule 



dorsal aorta 



intra-embryonic coelom 



extra-embryonic coelom 



Pig. 38. — Drawings from transverse sections to show the differentiation of the 



somites. 

 A, second somite of 4-somite chick; B, ninth somite of 12-somite chick; C, 

 twentieth somite of 30-somite chick; D, seventeenth somite of 33-somite chick. 



