26 THE NATURE OF LIFE 



of two cells called gametes. In the sim- 

 plest organisms these may be indistin- 

 guishable but in the course of evolution 

 one of the gametes becomes larger and 

 filled with stored nutriment : this is called 

 the egg. The other gamete remains small 

 and is frequently motile. 



The fusion of the gametes may be imi- 

 tated by drops consisting of artificial 

 mixtures which come together and unite. 

 Here surface forces are concerned as well 

 as the consistency of the protoplasm. 

 The process recalls the ingestion of bac- 

 teria by white blood cells, an operation 

 known as phagocytosis, which assists in 

 protecting the body from invasion by 

 bacteria. It has been suggested that 

 the fusion of gametes in the simplest 

 forms is allied to the process of ingesting 

 food. 



The fusion of the gametes is followed 

 sooner or later by the fusion of their 

 nuclei. As far as we can judge this is 

 subject to much the same forces as the 

 fusion of the gametes, but we have no 



