102 DEVELOPMENT OF BLOOD. 



three or four new cells, which gradually acquire the 

 characters of the original cell from which they sprang. 

 Fig. 30 (B, c, D, E.) 



Fig. 30.* 



D 



When, in the progress of embryonic development, the 

 liver begins to be formed, the multiplication of blood- 

 cells in the whole mass of blood ceases, according to 

 Kolliker, and new blood-cells are produced by this organ. 

 Like those just described, they are at first colourless and 

 nucleated, but afterwards acquire the ordinary blood- 

 tinge, and resemble very much those of the first set. Like 

 them they may also multiply by division. In whichever 

 way produced, however, whether from the original for- 

 mative cells of the embryo, or by the liver, these coloured 

 nucleated cells begin very early in foetal life to be mingled 

 with coloured non-nucleated corpuscles resembling those 

 of the adult, and about the second or third month of 

 embryonic existence are completely replaced by them. 



* Fig. 30. Development of tlie first set of blood-corpuscles in the 

 mammalian embryo. A. A dotted, nucleated embryo-cell in process of 

 conversion into a blood-corpuscle : the nucleus provided with a nucle- 

 olus. B. A similar cell with a dividing nucleus ; at c, the division of 

 the nucleus is complete ; at D, the cell also is dividing. E. A blood- 

 corpuscle almost complete, but still containing a few granules. F. Perfect 

 blood-corpuscle. 



