No. 644] ARRESTED EVOLUTION 



267 



the same colonial stock or neighboring colonial stocks of 

 plantations. The most important of the disadvantages 

 resulting from hermaphroditism would then be to reduce 

 the variability which is necessary to progress in the 

 struggle for existence. 



While, however, the possibility is not denied that fer- 

 tilization may be a controlling factor in variation, as 

 stated, e.g., by William E. Kellicott in his " Text-book 

 of General Embryology," 1913, p. 216, it is also obvious, 

 according to the same author, that the evidence for this 

 view is still scanty and uncertain and, moreover, there 

 are two exactly opposed views as to the nature of the 

 relation. While Hertwig maintains that the effect of 

 fertilization is to limit variation within a species, Weis- 

 mann asserts that the effect of syngamy or " amphi- 

 mixis " is to cause or promote variation. 



Kellicott {op. cit., p. 214) states: 



There is little direct factual evidence for or against these views, 

 either one of which can be maintained upon theoretical grounds. 

 In a few eases it is known that the amount of variability is not 

 significantly different among sexually (gametically) or asexually 

 (parthenogenetieally) produced individuals of the same species. And 

 from the standpoint of more recent studies upon heredity and varia- 

 tion the evidence is chiefly either negative or opposed to the idea 

 that this relation constitutes an important element m the origm or 

 present function of fertilization. The present aspects of this rela- 



of the relations with heredity. 



While among the higher classes fertilization has be- 

 come a stimulus to reproduction and a means of heredity, 

 evidence from the lower groups tends to show that fer- 

 tilization in its results has undergone evolution like ever\' 

 other organic function. 



The view is widely accepted today (see Kellicott, p. 

 209) that among the Protozoa the processes of reproduc- 

 tion and fertilization are not fundamentally related, and 

 the primary significance of fertilization must be sought 

 in some other direction. 



The observations made on protozoans have led to the 



