PREFACE XV 



wis with lyrate, wide-spreading horns and hairless pasterns 

 on both fore and hind feet. This arrangement shows at 

 once the true relationship of such a completely isolated 

 member of the lechwis as the Nile lechwi, Onotragus 

 megaceras, which is usually referred to as Mrs. Gray's water- 

 buck, an altogether meaningless and misleading name. 



We are well aware that objection may be taken to our 

 use of the words "species" and "genus." This is unavoid- 

 able, for as yet there is no general standard of agreement 

 as to their use. Of course "species" is an artificial term, 

 which, no matter how defined, can only approximately ex- 

 press the facts in nature. No definition will entirely and 

 precisely meet the case; and any limitation we use in defin- 

 ing species will still necessarily leave the term in one case 

 out of parallel with the term in another. If we had all the 

 connecting links before us it would be practically impossible 

 as regards any animal to do more than mark the "specific" 

 differences in purely artificial and conventional fashion; for 

 even if species are due to sudden mutations and not to in- 

 finitely slow changes, these mutations must, in the immense 

 majority of cases, each be so comparatively small that the 

 use of the word "species" would appear an exaggerated 

 way of noting the difi^erence. Moreover, as regards the 

 "species" of some animals, such as the arctogeal wolf — 

 including, say, the Texan, extreme boreal, and Indian forms 

 — and the common zebra or bonte-quagga, the gradations 

 are even at this stage of the world's history practically com- 

 plete between extremes which, if it were not for this inter- 

 grading, would unquestionably be accepted as specifically 

 distinct. It is impossible to arrange either species or sub- 

 species satisfactorily in linear fashion, so as to show the rela- 



