52 THE EVOLUTION OF MAN 



destroyed, little is known as to where or how the destructive 

 process occurs. Sometimes they seem to be destroyed much 

 faster than they are formed and this results in a great reduc- 

 tion of the number of the red blood cells of the body from 



Middle lobe 



of thyroid gland. 



Thymus gland. 

 Lateral lobe 



of thyroid gland. 



Trachea. 

 Lung. 



Right lobe of liver. 



Vitelline duct. 



Pharyngeal 

 pouches. 



Stomach. 



Pancreas. 



Left lobe of liver. 



Small intestine. 



Large intestine. 



Fig. 19. Organs developing from the rudi- 

 mentary alimentary canal. After Bonnet. 

 From Heisler, Embryology. By permission 

 of W. B. Saunders and Co. 



5,000,000 to perhaps 1,000,000 per cubic millimeter, together 

 with the appearance also of a certain number of the embry- 

 onic type of nucleated red cells in the blood stream. Evidently 

 the immature cells are drawn into the blood stream in the 

 endeavor to make good the excessive loss. This is the condi- 

 tion which exists in that quite fatal disease, pernicious anaemia. 



