THE INDIVIDUAL AND THE SPECIES 165 



begin to segment again and will reproduce the typical 

 larval Sea-urchin. The parasitic flat-worm, known 

 as the liver-fluke, produces larvae which develop to 

 form other larvae called rediae. Each redia normally 

 develops into another larval form, called a cercaria, 

 which Anally develops into the adult worm. But in 

 certain circumstances each redia may divide and 

 reproduce a number of daughter- rediae, and there may 

 even be several generations of these larvae. In many 

 lower animals buds may be formed from almost any 

 part of the body, and each of these buds may reproduce 

 the entire organism. In plants the entire organism 

 may be grown from a very restricted part or cutting. 

 Thus the individual, whether of the first, second, or 

 third order, may be divided without necessarily 

 ceasing to be what it was. 



Regeneration of fragments detached from the 

 fully developed adult body so as to form complete 

 organisms does not, in general, occur among the higher 

 animals, nor, as a general rule, does reproduction by 

 bud-formation occur. When such animals reproduce, 

 an ovum develops to form a large mass of cells, which 

 later on become differentiated to form the tissues and 

 organs of the adult body. But a relatively small 

 number of the undifferentiated cells persists in the 

 ovaries of the females, or in the testes of the males, 

 and each of these cells may again develop and reproduce 

 the organism. There is apparently no limit to this 

 process : any animal ovum may become divided 

 successively so that an infinite geometrical series is 

 produced, and in every term of this series all the 

 potentialities of the first one are contained. 



The physical concept of individuality — that which 

 cannot be divided, or which may not be divided with- 

 out ceasing to be what it was — such individuality as 



