SIMPLE CELLS. 12$ 



jntirely differently conceived. The cell is now usually 

 iefined as a small semi-solid or semi-fluid (i.e. neither solid 

 aor fluid) dense body, the chemical nature of which is albu- 

 ninous, and in which another small roundish body, generally 

 nore solid, and also albuminous, is enclosed. An envelope 

 or membrane may exist, as is the case with most plant- 

 cells ; but it may be wanting, as in most animal-cells. 

 Originally it is never present. The young cells are usually 

 i^oundish in form, but they afterwards vary very greatly. 

 The cells from different parts of the human body, repre- 

 sented in Figures 2-G, may be compared as examples. 



Fig. 4.— Five thorny, or heckle-cells, the edges of which fit into each 

 it her, from the epidermis ; one (h) is separated from the rest. 



The most essential feature in the modern conception of 

 :he cells is, therefore, that the cell-body is composed of two 

 listinct parts. The one constituent part is the inner, and 

 s called the nucleus (cytohlastus) ; this is generally of a 

 ound, oval, or spherical form, usually more solid, seldom 

 softer than the protoplasm, and consists of a peculiar 

 dbuminous substance, the nuclein or kernel-substance ; the 

 second essential constituent part of every cell is the cell- 

 dime or cell-substance — the protoplasm, or primitive slime 

 ' Urschleim of the older natural philosophers). This proto- 

 plasm, which surrounds the nucleus, also belongs, in point 

 i)f chemical composition, to the class of albuminous sub- 

 stances, and is a compound of carbon, containing some 



