22 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



idea of an individual living for itself. But it does 

 more than this ; it performs also the function that is 

 necessary for the continuance of the species of which 

 it is a representative. It reproduces itself. 



In the simplest case the act of reproduction is 

 effected thus ; the nucleus elongates, becomes con- 

 stricted in its middle, and divides into two. As this 

 division is being effected the surrounding protoplasm 

 becomes divided into two masses, each of which 

 accompanies one half of the nucleus. As a result of 

 this process we have two individuals where before 

 we had one, and they differ only from the amoeba 

 which we have been previously studying by their 

 smaller size ; as our first amoeba has altogether dis- 

 appeared, it is, to all practical purposes, dead ; and 

 we have, then, in this, the simplest condition of 

 reproduction, the death of the parent absolutely co- 

 temporaneous with the appearance of a new generation. 

 This process of reproduction is that which is known 

 as fission. 



Another method is also observed in the amoeba, 

 which may be regarded as a modification of that of 

 fission. A small portion (bud) of non-nucleated 

 protoplasm is gradually separated off from the rest of 

 the mass ; this increases in size, and develops within 

 itself a new nucleus, so that it becomes exactly 

 similar to its parent, which, in this case, continues to 

 exist. Here we have reproduction effected by bud- 

 ding, or gemmation. 



Notwithstanding all the functions performed by 

 this minute mass of protoplasm, it will be observed 

 that there is nothing in the cell to which we could 

 correctly give the name of an organ. We are in the 

 presence of life, but hardly of organisation. 



