THE EVOLUTION OF SEX 3 



ot vouch for them all, but whether they are en- 

 tirely correct or only partially so, they give a rough 

 idea at least of the stupendous power of growth. 



There are three checks to this process: First, the 

 food supply is insufficient you starve ; second, ani- 

 mals eat each other you feed ; third, substances are 

 produced by the activity of the body itself that inter- 

 fere with its powers of growth yoji poison yourself. 

 The laws of food supply and the appetites of enemies 

 are as inexorable as fate. Life may be defined as a 

 constant attempt to find the one and avoid the other. 

 But we are concerned here with the third point, the 

 methods that have been devised of escape from the 

 limitations of the body itself. This is found in repro- 

 duction. The simplest possible device is to divide. 

 This makes dispersal possible with an increased chance 

 of finding food, and of escaping annihilation, and at 

 the same time by reducing the mass permits of a more 

 ready escape of the by-products of the living machine. 



Reproduction by simple division is a well-known pro- 

 cess in many of the lower animals and plants; it is 

 almost universal in one-celled forms, and not unknown 

 even in many-celled organisms. Amoeba and para- 

 mcecium are the stock cases for unicellular animals; 

 many plants reproduce by buds, tubers, stolons, or 

 shoots ; hydroids and sea-anemones both divide and 

 bud ; many planarians, and some worms, divide trans- 

 versely to produce two new individuals. But these 

 methods of reproduction are limited to simple structures 

 where concentration and division of labor amongst the 

 organs has not been carried to an extreme. In con- 

 sequence, what each part lacks after the division can be 



