126 



SIMPLE HISTOLOGICAL ELEMENTS. 



Fig. 



each other, it finally separates into two distinct nucleolated cells. 



In the blood-corpuscles of the chick, all the stages of this process 



can be readily observed. 



This development of cells by bipartite 

 division occurs in the red blood-cor- 

 puscles of the embryos of birds and 

 mammalia, and in the first colorless cor- 

 puscles of the tadpole. (Fig. 66.) It also 

 occurs, probably, in the colorless blood- 

 corpuscles of the human embryo, and, 

 sometimes at least, in the chyle-cor- 

 puscles of adult animals. (KoUiker.) 

 It is also constantly observable in the development of cartilage 



(Figs. -67 and 46), and here the division may be bipartite, tripartite, 



or even tetrapartite. 



Fig. 67. 



Blood-corpuscles multiplying by bi- 

 partite division. (K^lliker.) 



Multiplication of cartilage-cells by division. 



THE PHYSIOLOGY OF CELLS. 

 Under this head will be considered 



A. The growth of cells. 



B. Their physiology proper, including the nature of their contents, 



and the processes performed by them. 



A. The Growth of Cells. 



Growth, doubtless, occurs in all cells, to some extent. It is, how- 

 ever, most manifest in cases when the cell-membrane is formed 



