DEVELOPMENT OF THE RED BLOOD CORPUSCLES 



129 



The red corpuscles are constantly undergoing disintegration in different 

 parts of the circulatory system, particularly in the spleen. The liberated 

 hemoglobin contributes to the formation of the bile pigments in the liver. 



Development of the Red Blood Corpuscles. The first formed 

 blood corpuscles of the human embryo differ much in their general characters 

 from those which belong to the later periods of intra-uterine, and to all 

 periods of extra-uterine life. Their manner of origin is at first very simple. 



Surrounding the early embryo is a circular area, called the vascular area 

 in which the first rudiments of the blood vessels and blood corpuscles are 

 developed. Here the nucleated embryonal cells of the mesoblast, from 

 which the blood vessels and corpuscles are to be formed, send out processes 

 in various directions, 

 and these, joining to- 

 gether, form an irregu- 

 lar mesh-work. The 

 nuclei increase in num- 

 ber, and collect chiefly 

 in the larger masses of 

 protoplasm, but partly 

 also in the processes. 

 It appears that hemo- 

 globin then makes its 

 appearance in certain 

 of these nucleated em- FIG. 112. Part of the Network of Developing Blood 



brvonal cells which Vessels in the Vascular Area of a Guinea-pig. Showing blood 

 corpuscles becoming free in an enlarged and hollowed-out 



thus become the earliest part of the network and processes of protoplasm. (E. A. 

 red blood corpuscles. Schafer.) 



The protoplasm of the cells and their branched network in which these, 

 corpuscles lie then become hollowed out into a system of canals enclosing 

 fluid in which the red nucleated corpuscles float. The corpuscles at first 

 are from about IOJJL to i6/< in diameter, mostly spherical, and with granular 

 contents, and a well-marked nucleus. Their nuclei, which are about 5^ 

 in diameter, are central, circular, very little prominent on the surfaces of 

 the corpuscles, and apparently slightly granular. 



The corpuscles then strongly resemble the colorless corpuscles of the 

 fully developed blood but for their color. They are capable of ameboid 

 movement and multiply by division. 



When, in the progress of embryonic development, the liver is formed, 

 the multiplication of blood-cells in the whole mass of blood ceases, and new 

 blood-cells are produced by this organ, and also by the spleen. These are 

 at first colorless and nucleated, but afterward acquire the ordinary blood 

 tinge, and resemble very much those of the first set. They also multiply by 

 division. The bone marrow also begins to form red corpuscles, though at 



