THE PROTOPLASMA AND THE CELL. 7 



external layers of the epidermis covering our skin (Fig. 11). 

 Other. -cells (Fig. 12) contain, in complete contrast, double 

 nuclei. Their signification will occupy us later. Very singu- 

 lar structures, of irregular form, and, in part, of extraordinary 



Fig. 11. — Non-nucleated cells 



of the epidermis. 



Fig. 12. — Cells with double nuclei : 

 a, from the liver, b from the choroid 

 of the eye, and c, from a ganglion. 



m 



Fio. 13. — Multi-nuclear giant 

 cell from the bone marrow of the 

 new-born. 



dimensions, occur in the bone marrow, and also in many ab- 

 normal tumors. They have been called myeloplaxes and 

 giant cells (Fig. 13). Their larger specimens may contain a 

 multitude of nuclei. 



In these two things, the protoplasm and the nucleus, we 

 have become acquainted with the essential constituents of 



the cell. 



The youthful cell shows nothing further. 



Later, it may become different. The surface of the cell 

 body hardens, or from this vicinity is formed a firmer envel- 

 oping layer. Thus we have, when this remains very thin, 

 what is called a cell membrane, while to a thicker covering is 

 given the name of the cell capsule. 



We just said, " this may occur ; " but it need not. At the 

 present time we occupy a standpoint different from that of 



