54 SCIENCE PROGRESS. 



pear, to justify the constitution of a species ? On these 

 weary questions volumes of controversy have been spent. 

 No general rule can be found, for no real distinction exists, 

 and in practice each man must follow his own standard. So 

 long, however, as each distinct form receives a separate 

 name by' which it can be known and treated of it matters 

 perhaps little whether it is reckoned as a species, sub- 

 species, " representative species," local race or variety. All 

 that we have to remember is that these various terms have 

 no precise signification. 



The existence of such local forms is nevertheless one of 

 the best possible points of departure for an attempt to study 

 the origin of species. In each case, where two local varie- 

 ties are known, the problem of the origin of species is pre- 

 sented in a particular form. How did those two particular 

 varieties A and B come into existence ? 



Causes apart, by what steps in descent was the one 

 produced from the other, or both from something else ? 

 These are nascent species if there are any on the earth. 

 Here if anywhere is our chance to see, if not the mode by 

 which species come into existence, at least the way in 

 which differentiated forms are connected together, and the 

 steps by which they may separate. It is true enough that 

 even in the case of most local races which are materially 

 distinct the evidence as to the connecting steps is gone. 

 In one locality one form is found, in another locality 

 another form. Each area is distinct and isolated, and has 

 its distinct population ; beyond that nothing is known. But 

 besides these there are other cases, rarer perhaps, but still 

 fairly numerous, in which local forms inhabit conterminous 

 areas, and, though distinct enough in their chief habitats, 

 yet meet each other and breed together in the intervening 

 district, producing offspring which we have no reason to 

 suppose infertile. Such cases have a prerogative claim on 

 the notice of the evolutionist. Two forms, each well de- 

 fined, each, as is presumed, adapted by its peculiarities to 

 its own area, meet in an intervening area. In what state 

 is that intervening population ? On seriation does it 

 appear that the population consists mainly of one normal 



