PROTOZOA 309 



precisely the duty of dissolving themselves ; and it is 

 possible that most cells only do their work so well at 

 the cost of using themselves up in the process. They 

 can do this, because the propagation of the species is 

 secured by the germ -cells, which perform their duty 

 the more confidently when the body they are in is in a 

 good condition. The more advanced the body is in 

 organisation, the better will be the nutrition of the germ 

 and the greater its security from dangers. 



It may be asked whether there is not some such division 

 of labour within the one cell of the protozoa ; whether 

 there are not in these animals also parts that can only 

 discharge their function for a certain time, and must then 

 decay and be reconstructed by the permanent parts of 

 the cell. 



This is really the case. In many of the protozoa only 

 the nucleus and a small part of the protoplasm are 

 divided in non-sexual multiplication, for the greater part 

 of the cell-body dies. Hence there are a number of 

 protozoa in which we constantly find dead parts. In 

 fact, it looks as if dead parts are continually being 

 extruded from all protozoa. It has been proved by 

 careful experiments that protozoa perish if they are 

 impeded in their amphimixis. Thus amphimixis is 

 necessary for the protozoa.-^ It is true that they usually 

 propagate asexually, but from time to time their body has 

 to effect an exchange of basic particles with another one. 



' I cannot go any further here into the introduction of amphimixis 

 into the organic world. Weismann has attempted to trace it to its 

 ultimate roots. He believes that it arose in the earliest, unnucleated 

 living things, and had a favourable influence on their metabolism. It 

 was, therefore, a process of adaptation. 



