3IO DARWINISM AND THE PROBLEMS OF LIFE 



But if any protozoa must submit to amphimixis in 

 order to preserve the species, there are in the group 

 parts that are subject to natural death. We have 

 described above how in the amphimixis of the unicellulars 

 the large nucleus, which undertakes the vital functions, 

 dissolves, and thus represents the corpse. It does not 

 alter the case essentially that this corpse is small in pro- 

 portion to the animal ; in many of the higher animals 

 the germ-cells are much larger than the body — as in the 

 case of the frog's eggs. The question is whether there 

 are any animals whose whole substance lives on con- 

 tinuously and is not dissolved by its metabolism. 

 That is clearly not the case with the protozoa. We are, 

 therefore, not justified in drawing a line between the 

 unicellulars and multicellulars, and saying that the former 

 are immortal and the latter not. 



However, the protozoa are not the lowest organisms. 

 In them the living matter is already differentiated, 

 particularly into nucleus and cell-body. In our view 

 there must have been animals from the beginning of 

 life in which there was no differentiation. It is a 

 question whether there are now any unnucleated 

 organisms of this kind, as a nucleus has been found 

 even in the smallest animals. That is, of course, not 

 conclusive, because the simplest living things may be 

 below the limit of visibility. However that may be, we 

 can at least picture to ourselves animals whose repro- 

 duction consists merely in dividing without leaving any 

 residue, and in which there is not any amphimixis. 

 We must not forget, of course, that even in such 

 animals the living matter as such is not immortal, 



