168 



THE AMERICAN NATURALIST [Vol. XLIII 



world is alluded to. This gives the rank of species to the 

 forms which differ by characters never varying on the 

 same tree and never found connected by intermediate 

 states. Out of 300 species at least two thirds are pro- 

 visional species. Thus Quercus robur has twenty-eight 

 varieties, all of which, excepting six, are clustered 

 round three subspecies. 



Commenting on this condition of things, that is, where 

 there is no clear line of demarcation between species and 

 subspecies, and between subspecies and varieties, or be- 

 tween lesser varieties and individual differences, he thus 

 concludes : 



Hence I look at individual differences, though of small interest to 

 the systematist, as of the highest importance to us, as being the first 

 steps towards such slight varieties as are barely thought worth record- 

 ing in works on natural history, and I look on varieties which are in 

 any degree more distinct and permanent, as steps towards more strongly- 

 marked and permanent varieties; and at the latter as leading to sub- 

 species, and then to species (pp. 41-2). 



A well marked variety may therefore be called an incipient species; 

 but whether this belief is justifiable must be judged by the weight of the 

 various facts and considerations to be given throughout this work 

 (P- 42). 



Darwin noticed that wide-ranging, much-diffused and 

 common species vary most; also that species of the larger 

 genera in each country vary more frequently than the 

 species of the smaller genera ; further, that many of the 

 species included within the larger genera resemble vari- 

 eties in being very closely, but unequally related to each 

 other, and in having restricted range (pp. 42-45). 



The following sentence is interesting in this connection: 



Every one who believes in slow and gradual evolution, will of course 

 admit, that specific characters may have been as abrupt and as great as 

 any single variation which we meet with under nature or even under 

 domestication. 



The above-quoted sentence follows a notice of Mivart's 

 belief that new species manifest themselves with sudden- 

 ness and by modifications beginning at once, of which 

 Darwin says: 



