THE EVOLUTION OF LIVING BEINGS. 91 



just as will happen in nature, and so continue to cre- 

 ate yearly a number of new types which are able to 

 fill a good many opportunities for existence, present in 

 their neighbourhood or within a distance to which 

 their seeds may be carried, thus offering in other 

 words, splendid material for adaptation. 



What is born, consequently depends on what is crossed, 

 what survives, on the local circumstances of the birth-place 

 of the new forms and on those of its neighbourhood. 



If the same kind of cross takes place in Japan and in 

 Holland, the same forms will be born at those two 

 distant places. So I found f. i. a white Mus rattus 

 with a brown head and brown shoulders caught in 

 Leiden, hardly distinctible from a similar form from 

 Japan in the Leiden Museum . 



As the Linneon Mus rattus ranges from Holland to 

 Japan, it evidently gives rise to the same recessive 

 forms, when two hybrids indistinctible from the black 

 dominants pair, irrespective of the spot where this 

 pairing takes place. 



Now it might very well happen, that the black form 

 disappeared from Japan and survived in Holland, 

 through local conditions favoring the survival of the 

 recessive form in Japan, in which case these two forms 

 would be considered as different ,,species", in support 

 of which distinction, one would not fail to lay stress upon 

 their occurence in very distant, not overlapping areas. 



Such a thing will happen especially frequently with 

 Linneons of plants, containing forms of a different de- 

 gree of resistancy against frost which leads to a diffe- 

 rence in the composition of such Linneons in different 



