342 A HISTORY OF BIRDS 



always fertile when crossed. Natural species are said to be 

 physiological species, as distinct from the morphological species 

 of the breeder. This was Huxley's contention. 



But as a matter of fact presumably " physiological " species 

 often prove, when put to the test, to be syngamic, that is to say, 

 fertile inter se. Nowhere is this more true than among the 

 Galli and Anatidse, while many Passerines show the same 

 fusibility, e.g., the Carrion and Hooded Crows (see p. 301). 

 The more closely, in short, any given "species" is studied the 

 more does this supposed infertility between it and its near 

 allies break down. We are beginning to realise that, as 

 Sir Ray Lankester long ago contended, the old conception of 

 species must go, and with it must go the word " species " 

 itself. In its place he would substitute the word " forms ". 

 Modern zoology furnishes abundant evidence in favour of this 

 view. For any given " species," if carefully studied, will be 

 found to be divisible into a number of geographical " races," 

 often differing one from another only in intensity of colour. 

 The number of these races or sub-species, as they are called, are 

 being constantly multiplied as closer scrutiny is brought to bear 

 upon them, and as a consequence the term " species " is in 

 proportion losing its significance. 



Yet the existence of asyngamic forms — forms which, while 

 obviously related, are yet infertile when crossed — as well as of 

 forms with no very near allies, cannot be controverted. These 

 are to be regarded as so many isolated geographical races 

 whose annectent members have perished, and they might well 

 be distinguished by some special term were it not for the 

 fact that it is at present, and is always likely to be, impossible in 

 the vast majority of cases to discover which are and which are 

 not asyngamic. Undoubtedly it would be a good thing to 

 abandon the word " species," substituting therefor some term 

 capable of embracing within its meaning what are now called 

 "good species " and all the variants thereof. But such a word 

 would really have connote generic rather than specific value, as 

 these terms are now understood, and there is little likelihood of 

 such a drastic step being taken by the present generation of 

 biologists. 



