194 THE PHILOSOPHY OF BIOLOGY 



species therefore differs a little in respect of all its 

 characters from the species from which it arose, or 

 from the other elementary species near which it is 

 situated. This is what we do usually find in the 

 cases of the " races," or " local varieties," of any one 

 common species of plant or animal. That we do not re- 

 cognise that most, or perhaps all, of the species known 

 to systematic biology are really composed of such local 

 races is merely because such results involve an amount 

 of close investigation such as has not generally been 

 possible except in the few cases studied with the object 

 of proving such variability ; or in the case of those 

 species which are studied with great attention to detail 

 because of their economic importance. Thus the 

 herrings of North European seas can be divided into 

 such races, and it is possible for a person possessing great 

 familiarity with these fishes to identify the various 

 races or elementary species that is, to name the 

 locality from which the fish were taken by considering 

 the characteristics in respect of which the herrings of 

 one part of the sea differ from those of other parts. 



The term " variety ' has rather a different con- 

 notation in systematic biology from that which is 

 included by the term ' elementary species." The 

 meaning of the latter is simple and clear. Two or 

 more elementary species are assemblages of organisms, 

 in each of which assemblages the mean positions 

 about which the various characters fluctuate is diff- 

 erent. The term " variety " cannot so easily be defined. 

 The progeny of two different species (in the sense of 

 the term as it is usually applied by systematists) 

 may be called a hybrid variety of one or other of the 

 parent species. In the case of the ordinary species 

 of zoology such a hybrid would, in general, be infertile, 

 or if it did produce offspring these would be infertile. 



