The Story of Evolution 69 



free. A big sea-anemone may divide in two or more parts, which 

 become separate animals. This is asexual reproduction, which 

 means that the multiplication takes place by dividing into two 

 or many portions, and not by liberating egg-cells and sperm-cells. 

 Among animals as among plants, asexual reproduction is very 

 common. But it has great disadvantages, for it is apt to be 

 physiologically expensive, and it is beset with difficulties when 

 the body shows great division of labour, and is very intimately 

 bound into unity. Thus, no one can think of a bee or a bird 

 multiplying by division or by budding. Moreover, if the body of 

 the parent has suffered from injury or deterioration, the result 

 of this is bound to be handed on to the next generation if asexual 

 reproduction is the only method. 



Splitting into two or many parts was the old-fashioned way 

 of multiplying, but one of the great steps in evolution was the 

 discovery of a better method, namely, sexual reproduction. The 

 gist of this is simply that during the process of body-building 

 (by the development of the fertilised egg-cell) certain units, 

 the germ-cells., do not share in forming ordinary tissues or organs, 

 but remain apart, continuing the full inheritance which was con- 

 densed in the fertilised egg-cell. These cells kept by them- 

 selves are the originators of the future reproductive cells of the 

 mature animal; they give rise to the egg-cells and the sperm- 

 cells. 



The advantages of this method are great. (1) The new 

 generation is started less expensively, for it is easier to shed germ- 

 cells into the cradle of the water than to separate off half of the 

 body. (2) It is possible to start a great many new lives at once, 

 and this may be of vital importance when the struggle for exist- 

 ence is very keen, and when parental care is impossible. (3) 

 The germ-cells are little likely to be prejudicially affected by 

 disadvantageous dints impressed on the body of the parent- 

 little likely unless the dints have peculiarly penetrating con- 

 sequences, as in the case of poisons. (4) A further advantage is 



