CH. xxvi.J DEVELOPMENT OF BLOOD-CORPUSCLES. 423 



these, joining together, form an irregular meshwork.' The 

 nuclei increase in number, and collect chiefly in the larger 

 masses of protoplasm, but partly also in the processes. These 

 nuclei gather around them a certain amount of the protoplasm, 

 and, becoming coloured, form the red blood corpuscles. 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 3.^0 to y^Vir f 

 an inch (lOfj. to i6/x) in diameter, mostly spherical, and with 

 granular contents, and a well-marked nucleus. Their nuclei, 



>8- 355- Part of the network of developing blood-vcKseln in the vascular area of a 

 guinea-pig. '</. blood-corpuscles becoming free in an enlarged and hollowed-otit part 

 of the network ; a, process of protoplasm. (E. A. Schafer.) 



which are about 5o 1 oo of an inch (5/4) in diameter, are central 

 and circular. 



The corpuscles then strongly resemble the colourless corpuscles 

 of the fully developed blood, but are coloured. They are capable 

 of amoeboid movement and multiply by division. 



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, and new blood-cells are produced by this 

 organ, and also by the lymphatic glands, thymus and spleen. 

 These are at first colourless and nucleated, but afterwards acquire 

 the ordinary blood-tinge, and resemble very much those of the 

 first set. They also multiply by division. In whichever way 

 produced, however, whether from the original formative cells of 

 the embryo, or by the liver and the other organs mentioned 

 above, these coloured nucleated cells begin very early in foetal life 

 to be mingled with coloured non-nucleated corpuscles resembling 



