212 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



individuals, but on the number of cell-generations, and that 

 continuous life is rendered possible by the reappearance of 

 amphimixis after each million or hundred thousand generations 

 of cells. We might also — as I have already mentioned— com- 

 pare the ' agamic ' cell-generations of Infusoria, which follow 

 each other between two periods of conjugation, with the collec- 

 tion of cells composing the person of a Metazoon, and regard 

 the ontogenetic cell-series, as a whole, as the equivalent of the 

 millions of individuals which make up an Infusorian colony. In 

 both these cases the rejuvenating and quickening influence of 

 amphimixis may be supposed to endure for a certain number of 

 cell-generations. I must admit that I consider such reasoning 

 to be bad ' philosophy of nature,' i. e. playing with words 

 which convey no distinct meaning. It is contradicted by the 

 fact that the cell-cycle of ontogeny in the lowest representative 

 of the Vertebrata, the Amphioxus, cannot be compared as 

 to length with that of the higher members of the group ; it is 

 equally disproved by the phenomena of cychcal development, 

 showing that in one case the effects of fertilization may extend 

 through one ontogeny, in another through two, three, six, or 

 even ten ontogenies, not to mention the case in which forty 

 generations have elapsed without the occurrence of amphimixis. 



If we regard amphimixis as an adaptation of the highest 

 importance, the phenomena can be explained in a simple way. 

 I only assume that amphimixis is of advantage in the phyletic 

 development of life, and furthermore that it is beneficial in 

 maintaining the level of adaptation, which has been once attained, 

 in every single organism ; for this is as dependent upon the 

 continuous activity of natural selection as the coining of new 

 species. According to the frequency with which amphimixis 

 recurs in the life of a species, is the efficiency with which the 

 species is maintained ; since so much the more easily will it 

 adapt itself to new conditions of life, and thus become modified. 



Amphimixis must first have appeared among unicellular or- 

 ganisms in the form in which we now find it in most Protozoa 

 (Flagellata, Sporozoa, Rhizopoda) -namely, as the complete 

 fusion of two entire animals \ 



^ Maupas (op. cit. p. 492") attributes to me the view that conjugation 

 bears a different significance in the lower Protozoa from that which it 

 possesses in the higher, and he describes this ' maniere de voir ' as 



