1^2 



THE EVOLUTION OF MAN. 



out and draws back again, iinger-like processes, thereby 

 modifying its form (Fig. 9)* Finally, the young cell has 



Fig. 9.— Active cells from the 

 inflamed ejc of a Frog (from the 

 watery moisture of the eye, the 

 humor aqueus). The naked cells 

 move freely and creep about ; 

 like Amcebas and Ehizopods they 

 accomplish this by extending deli- 

 cate processes from their naked 

 protoplasmic bodies. These pro- 

 cesses continually alter in number, 

 form, and size. The kernel of these 

 amoeboid lymph-cells is not visible, 

 being covered by the numerous deli- 

 cate granules which arc scattered 

 in the protoplasm. (After Frey.) 



feeling, and is more or less sensitive. It performs certain 

 movements on the application of chemical and mechanical 

 irritants. Thus we can trace in every single cell all the 

 essential functions, the sum of which constitute the idea of 

 life : feeling, motion, nutrition, reproduction. All these 

 properties which the multi-cellular, highly developed animal 

 possesses, appear in each separate cell, at least in its youth. 

 Tliere is no longer any doubt about this fact, and w^e may 

 therefore regard it as the basis of our physiological idea of 

 the elementary organism. 



Without lin^erinfj here over the extremelv interest- 

 ing phenomena of cell-life, we will at once attempt to 

 apply the Cell Theory to the egg. The comparison wdiich 

 we have made leads to the important result that we 

 must regard every egg as originally a simple cell. This 

 is of the highest significance, because the whole Science of 



