222 AMPHIMIXIS. 



further been shown that its occurrence in the Hfe of a species 

 becomes more frequent according as its admission by the vital 

 conditions does not entail other disadvantages. When neither 

 the formation of stocks nor the most rapid multiplication of 

 individuals in the shortest time is required, we find amphimixis 

 connected with the origin of every new individual ; but when- 

 ever the existence of the species would be endangered if new 

 generations could not arise from the old in the most rapid 

 succession and without any interval, we find that amphimixis 

 is not inseparably associated with every act of reproduction, 

 but makes its appearance only in certain generations. All 

 this clearly points to the conclusion that amphimixis is no 

 indispensable vital condition, no renewal of life or ' rejuven- 

 escence,' but a process which has indeed a deep significance, 

 although it is not inseparable from the continuance of vital 

 processes. This conclusion becomes even more evident when 

 we recognize how precisely, in the alternation of agamic and 

 sexual reproduction, the number of agamic generations is 

 regulated so as to correspond with the conditions of the species. 

 The rare or frequent repetition of amphimixis in the life-history 

 of a species is not determined by its physical nature but by the 

 conditions of life. Its regulation depends upon adaptation ; it 

 may be entirely excluded and the life of the species still 

 continues. I do not know of any facts which lead us, after 

 recognizing all this, to assume that amphimixis is anything 

 more than an essential advantage in the maintenance and modifi- 

 cation of species. 



