196 GENERAL BIOLOGY 



becomes more and more restricted through the estab- 

 lishment of a definite physical or chemical cause for 

 what had been thought to have a vitalistic explana- 

 tion, while never in the history of science has any 

 phenomenon, once explained on a physical or chemi- 

 cal basis, later been found to be vitalistic." 1 



Summary. In each species of plant or animal 

 there is a continuous and unbroken succession of 

 individuals that constantly replace one another. 

 There is no authentic instance of any individual 

 form of life coming into existence except from a 

 preexisting individual. The reproductive process 

 is essentially one of discontinuous growth. In its 

 simplest expression it involves the cutting in two of 

 a parent organism to produce two " daughter " 

 individuals. Instead of a half of the parent organ- 

 ism, the source of the i\ew individual may be a por- 

 tion of the parental tissue (bud) or a single cell 

 (spore or gamete). In the case of the spore the 

 new individual arises by direct growth and meta- 

 morphosis, but in the case of the gamete it arises 

 from a zygote, which is the result of the partial or 

 complete fusion of two gametes. In any event the 

 specific form of the new individual is attained by 

 differentiation from a relatively generalized to a 



1 The author is aware that the above paragraph gives a very incomplete 

 presentation of the vitalistic standpoint, particularly of that of the so- 

 called Neo-Vitalists. There are many kinds and degrees of vitalism, but 

 to go into the subject in detail is quite outside the compass of a work of 

 this sort. The interested student is referred to the works of Driesch, 

 Bergson, Reinke, Lovejoy, etc. 



