CHAPTER VIII. 

 THE LIMITS OF LINNEONS. 



That Linneons are more or less distinctly limited, 

 is apparent from the fact that in subdi vising the 

 living Kingdom, one made unconsciously halt at the 

 border of each Linneon, and so was led to consider 

 them as real species, such as Linnaeus beUeved them 

 to be. 



In most cases the limits between the smaller units 

 within the Linneon, are much less conspicuous, so that 

 it lasted until the middle of the 19th century before 

 Jordan discovered even the mere existence of such 

 smaller units within the Linneon. 



This difference in the distinctness of the limits between 

 the Jordanons and the Linneons needs explaining. 



We must enquire into this question by askiag: are 

 there cases, in which the Jordanons within a Linneon 

 are as distinct as the Linneons themselves and are 

 there cases in which this is not the case? 



The answer is that there are, so that the question 

 remains, what causes this difference? 



Investigation shows that poor distinctness of the Jor- 

 danons within the Linneon, occurs in all cases where these 

 Jordanons intercross freely and selection favors a certain 

 t5^e, and that this distinctness increases in the same ra- 

 tio as intercrossing decreases, so that it reaches its maxi- 

 mum when crossing does not occur at all, as in those cases 



