REPRODUCTION 257 



Certain other sorts. The multiplication of the individuals of 

 one species may often result in an increase in the number 

 of living organisms in the locality, but there is no evidence 

 that, as a whole, the living population of the earth is in- 

 creased. Keproduction is not a process by which more is 

 made out of a given amount, for, if this were so, the be- 

 ginning would be the making of something from nothing. 

 Force and matter remaining constant, reproduction can 

 only maintain, it cannot, beyond a certain point, increase 

 the total number of living organisms. 



We are thus led to see that reproduction is a process of 

 which the chief end is maintenance and increase of the spe- 

 cies rather than the increase in life. The command "Be 

 fruitful and multiply" is coupled with the law which irre- 

 sistibly forbids increase beyond a certain point. As char- 

 acteristic of the living substance as breathing or feeding is 

 the tendency to maintain and to perpetuate itself. Only by 

 securing more supplies of matter for replacing worn-out 

 parts, and of energy for carrying on its functions, does the 

 living organism maintain itself. When it secures more mat- 

 ter than is needed to repair, and more energy than is 

 needed to operate, already existing parts, it grows. WTien 

 for any reason growth beyond a certain characteristic size 

 is impossible or difficult, while the supply of matter and 

 energy continues the same, there must be some other mode 

 of increase of the individual, whether cell or organism. 

 The one individual, cell or organism, after forming new sub- 

 stance (protoplasm) and furnishing it with energy (heat, 

 etc.), may finally separate this as a new individual. The 

 mother cell divides it off as a new cell, the parent organism 

 separates it as a reproductive body, a sperm or egg, a 

 spore or seed, an embryo or a larva. Reproduction has 

 been defined as "Growth beyond the limits of the indi- 

 vidual." Like growth, it depends upon the successful per- 

 formance of the ordinary functions, and it simply insures 

 their continuance. 



Again, reproduction is said to be "the effort to bridge the 

 gap of death." This definition is suggestive but misleading. 

 By reproduction living is continued ; the life, the substance, 



