368 



COMPARATIVE ANATOMY 



short — possibly a month. The first enucleated erythrocytes appear 

 during the second month, mostly from the liver. Up until that time all 

 embryonic blood cells are nucleated, as in the adults of lower vertebrates. 



neural plate ectoderm 

 dorsal mesoderm 



superficial ectoderm 

 neural groove 



] — somatopleure 

 splanchnopleure 



splanchnic mesoderm 



gut imrnedia&ely caudal t 

 anterior intestinal portal 



dorsal mesoderm 



epi-myocardium 



endocardium ^ g^t immediately caudal to 

 anterior intestinal portal 



> somatopleure 



y splanchnopleure 



epi-myocardium 

 endocardium 



dorsal mesoderm 



epi-myocard: 



endocardium 



I — somatopleure 

 J- splanchnopleure 



Ime offusionof lateral margins of 

 anterior intestinal portal 



dorsal mesoderm 



D 



fore-gut 



dorsal mesocardium 



J— somatopleure 



.J- splanchnopleure 

 epi-myocardium 



ventral mesocardium 



endocardium 



E 



dorsal mesoderm 

 notochord 



dorsal mesocard: 



somatopleure 



J — splanchnopleure 



epi-myocardium 



Fig. 306. — Diagrams of transverse sections through the pericardial region of chicks 

 at various stages to show the formation of the heart. A, at 25 hours; B. at 26 hours; C, 

 at 27 hours; D, at 28 hours; £, at 29 hours. (From Patten's ** Embryology of the 

 Chick.") 



White blood corpuscles are of two types, granular and non-granular. 

 Most of the non-granular are lymphocytes which have about the same 



