460 Mutations 



ently lost character. The elenientary species, 

 on the other hand, must have arisen by the pro- 

 duction of new qualities, each new acquisition 

 constituting the origin of a new elementary 

 form. 



Moreover we have seen, that such improve- 

 ments and such losses constitute sharp limits 

 between the single unit-forms. Every type, of 

 course, varies around an average, and the ex- 

 tremes of one form may sometimes reach or 

 even overlap those of the nearest allies, but 

 the offspring of the extremes always return to 

 the type. The transgression is only temporary 

 and a real transition of one form to another 

 does not come within ordinary features of fluc- 

 tuating variability. Even in the cases of ever- 

 sporting varieties, where two opposite types 

 are united within one race, and where the suc- 

 ceeding individuals are continually swinging 

 from one extreme to the other, passing through 

 a wide range of intermediate steps, the limits 

 of the variety are as sharply defined and as free 

 from real transgression as in any other form. 



In a complete systematic enumeration of the 

 real units of nature, the elementary species and 

 varieties are thus observed to be discontinous 

 and separated by definite gaps. Every unit 

 may have its youth, may lead a long life in the 

 adult state and may finally die. But through 



