82 THE ANIMALS AND MAN 



form the other life-processes, such as taking and digesting 

 food, breathing and feeling, in an extremely primitive simple 

 way, so do they perform the necessary life-process of re- 

 production or multiplication in the simplest way shown 

 among animals. 



In the case of Paramoscium the process of multiplication 

 is slightly more complex than that of AmcBha in the fact 

 that sometimes before the simple fission of the body takes 

 place the interesting phenomenon of conjugation occurs. 

 If the two conjugating individuals differ at all — and they 

 always do differ, because no two individual animals, al- 

 though belonging to the same species, are exactly alike — 

 the new individual, made up of parts of each of them, will 

 differ slightly from both. Nature seems intent on making 

 every new individual differ slightly from the individual 

 which precedes it. And the method of multiplication which 

 Nature has adopted to produce the result is the method which 

 we have seen exhibited in its simplest form in the case of 

 ParanuBcium — the method of having two individuals take 

 part in the production of a new one. 



The development of the new Paramcecia is a litde more 

 complex than that of Amceba. Not only must the new 

 Paramcecium grow to the size of the original one, but it 

 must develop those slight, but apparent, modifications of 

 the parts of its body which we can recognize in the full- 

 grown, fully developed Paramoscium individual. A new 

 mouth-opening must develop on the new individual formed 

 of the hinder half of the original Paramecium and new 

 cilia must be developed. And the recent studies of a careful 

 naturalist have shown that altogether the new Paramcecia 

 undergo considerable change during their growth to full size. 

 Thus there is a slight advance in complexity of development, 

 just as there is in complexity of structure in Paramoscium as 

 compared with Amceba. In the many-celled animals this 

 complexity of development is carried to an extreme. 



