The Nature of Animal Life. 



n 



by special changes in the nucleus (which also divides) and 

 by the arrangement of its network or filaments into the 

 rosettes and stars before alluded to. 



Instead, therefore, of the somewhat vague statement 

 that animals are made of flesh and blood, we may now say 

 that the living substance of which animals are composed 

 is a complex material called protoplasm ; that organisms 

 are formed either of single cells or of a number of related 

 cells, together with certain life-products of these cells ; and 



c.m. 



n.wt. 



Fig. 3. A cell, greatly magnified. 



c. m., cell-membrane; c.p., cell-protoplasm ; n.m., nuclear membrane ; n.p., nuclear proto- 

 plasm ; n.f., coiled nuclear filament. 



that each cell, small as it is, has a definite and wonderful 

 minute structure revealed by the microscope. 



9. Animals grow old and die. This is a familar obser- 

 vation. Apart from the fact that they are often killed by 

 accident, by the teeth or claws of an enemy, or by disease, 

 animals, like human beings, in course of time become less 

 active and less vigorous ; the vital forces gradually fail, 

 and eventually the flame of life, which has for some time 

 been burning dimmer and dimmer, flickers out and dies. 

 But is this true of all animals ? Can we say that death 

 as distinct from being killed is the natural heritage of 

 every creature that lives ? 



