l6o THE EVOLUTION OF LIVING BEINGS. 



finally lead to extinction of the classes also. There is 

 consequently periodicity in the production of new 

 types, no matter whether these are so different that we 

 put them into different classes, or so little different that 

 we put them into different Linneons only. 



Such a period of production of new types is always 

 immediately followed by the beginning of extinction 

 through the struggle for life, which is withstood as long 

 as crossing remains possible, and becomes complete 

 sooner or later, after the last possibility of a cross has 

 disappeared. 



Selection is only ,,une belle phrase" for extinction, the 

 forms last exterminated, being called the selected ones. 



Adaptation has a double meaning: adaptation of Lin- 

 neons to changed conditions by changing their internal 

 composition through the production of new types as the 

 result of crossing, which do not transgress the limits the 

 Linneon and adaptation of individuals by the plasticity 

 which every individual enjoys, within limits, to respond 

 to the call of new necessities. 



The vera causa of the production of new types conse- 

 quently is : crossing ; the vera causa of their extinction : 

 the struggle for life ; the selection resulting from the latter, 

 is by no means a revival, but is the sign of struggle of the 

 doomed. 



The production of new classes can evidently only be 

 studied and demonstrated experimentally in a period of 

 production of such classes; in a period, as the present one, 

 we must be content with the demonstration of the origin of 



