( ci ) 



difPerences in the skeletons of domestic rabbits. I showed 

 some of the points to Waterhouse, and asked him whether he 

 could pretend that they were not as great as between species, 

 and he answered, ' They are a great deal more.' How very odd 

 that no zoologist should ever have thought it worth while to look 

 to the real structure of varieties. . . ." * Then again, the differ- 

 ences between many of our domestic breeds, and between them 

 and the nearest wild species, are, as is well known, generic rather 

 than specific. Why do we not consider such races to be of 

 different species and genera ? Because of the criterion sug- 

 gested by Lankester ; because we have reason to believe in 

 their descent from common parents within the historic period ; 

 because, in spite of their wide differences, they are still 

 syngamic. 



What is the practical bearing of these criticisms upon the 

 definition of species by diagnosis and diagnosis alone 1 The 

 systematist, confronted by his series of specimens in a museum 

 cannot do otherwise than arrange them in groups which he 

 will describe and name as species. But much' would be gained 

 if he admitted at the outset that his conclusions are provisional, 

 if he said with Dr. Karl Jordan, " The actual proof of .specific 

 distinctness the .systematist as such cannot bring ; ... we 

 work, or we ought to work, with the mental re.servation that 

 the specific distinctness of our species novx deduced from 

 morphological differences will be corroboiuted by biology." t 



The advantage of this attitude is obvious. Work would go on 

 as at present. Powers of acute observation and good judg- 

 ment would still furnish descriptions of species to be hereafter 

 confirmed, or confirmed at the time by observation and experi- 

 ment upon the living material. But the systematist would 

 not only receive our gratitude for the performance of these 

 important and necessary duties : he would also be seeking in 

 every direction for the evidence of syngamy and of epigony. 

 The museum would become a centre for the inspiration of 

 researches of the highest interest to the investigator himself, 

 of the greatest importance to the whole body of naturalists. 



* " More Letters," vol. ii, p. 210, Letter 543. 



t "Novitates Zoologicse," vol. ill, Dec. 1896, pp. 450, 451. I liere 

 desire to express my indebtedness to the author of this learned and valuable 

 paper. 



