Chap. II. DOUBTFUL SPECIES. 47 



Those forms which possess in some considerable 

 degree the character of species, but which are so closely- 

 similar to some other forms, or are so closely linked to 

 them by intermediate gradations, that naturalists do not 

 like to rank them as distinct species, are in several re- 

 spects the most important for us. We have every reason 

 to believe that many of these doubtful and closely-allied 

 forms have permanently retained their characters in 

 their own country for a long time ; for as long, as far 

 as we know, as have good and true species. Practi- 

 cally, when a naturalist can unite two forms together 

 by others having intermediate characters, he treats the 

 one as a variety of the other, ranking the most common, 

 but sometimes the one first described, as the species, 

 and the other as the variety. But cases of great diffi- 

 culty, which I will not here enumerate, sometimes 

 occur in deciding whether or not to rank one form as 

 a variety of another, even when they are closely con- 

 nected by intermediate links ; nor will the commonly- 

 assumed hybrid nature of the intermediate links always 

 remove the difficulty. In very many cases, however, 

 one form is ranked as a variety of another, not because 

 the intermediate links have actually been found, but 

 because analogy leads the observer to suppose either 

 that they do now somewhere exist, or may formerly 

 have existed ; and here a wide door for the entry of 

 doubt and conjecture is opened. 



Hence, in determining whether a form should be 

 ranked as a species or a variety, the opinion of natural- 

 ists having sound judgment and wide experience seems 

 the only guide to follow. We must, however, in many 

 cases, decide by a majority of naturalists, for few well- 

 marked and well-known varieties can be named which 

 have not been ranked as species by at least some com- 

 petent judges. 



