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differences 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? The 
systematist, confronted by his series of specimens in a museum 
cannot do otherwise than arrange them in groups which he 
will describe and nameas 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 reservation that 
the specific distinctness of our species nove deduced from 
morphological differences will be corroborated by biology.” + 
The advantage of thisattitudeis obvious. Work would goon 
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. 
+ “Novitates Zoologice,” vol. iii, Dec. 1896, pp. 450, 451. I here 
desire to express my indebtedness to the author of this learned and valuable 
paper. 
