THE P ROTO PLASMA AND THE CELL. 



5 



which in a momentous manner the bodies of all the higher 

 animals have proceeded, the ovum (Fig. 5), 

 presents itself as an elegant spheroidal 

 structure. 



From this primitive form two other 

 forms, resulting from compression and 

 adaptation, may be readily traced ; the 

 tall, slender, or, as we say, cylindrical cell 

 (Fig. 6, b), and the flattened. The latter 

 finally assumes the form of a lamella or 

 scale (Fig. 7). 



The bodies of other cells grow in two 

 opposite directions, like processes. We 

 thus obtain the spindle-shaped cell (Fig. 

 4, c, f). When such processes are numer- 

 ous and are also branched, a singular thing 

 appears, the stellate cell (Fig. 8). 



Fig. 5. — Young ova, 

 from the ovarium of a 

 rabbit. 



Fig. 6. — Cylindrical cell-, from the human small 

 intestine; 6, ordinary elements ; a, so-calkd 

 Kecher-cells. 



Fig. 7. — Epithelial scales from the 

 human mouth. 



The quantity of the cell protoplasma, and hence 

 the magnitude of the body of the cell, is subject 

 to great variation (Fig. 4). 



While protoplasma occurs originally in every cell, 

 it may subsequently be replaced by other materials. 

 Thus, in the cells of our Fig. 7, a harder, more water- 

 less substance — keratine — has been substituted. 

 Other cells obtain a lodgment of dark, black pig- a , an ' d vmpha 

 ment granules of great chemical resistance (Fig. 9). 

 These dark molecules are called melanin. One of the 

 most widely diffused structures of the human body is the 



Fig. 8.— Stel- 

 late cell from 

 lie 



