1896 | LHE PHILOSOPHY OF SPECIES-MAKING 457 
means of classifying our knowledge of nature, and are not enti- 
ties in themselves. Species are, therefore, a human contrivance, 
and the only value which the modern naturalist can attach to 
them, as such, is their temporary convenience as a means and 
vehicle of thinking and writing about the organic creation. They 
should be defined only in terms of classification, not in terms of 
structure and genealogy, that is, in terms extrinsic, not terms 
intrinsic. Modern naturalists have largely eliminated genealogy 
from the definitions of species, but I do not recall any who define 
it solely as a convenience of taxonomy. Huxley writes that ‘a 
species is the smallest group to which distinctive and invariable 
characters can be assigned.’’ Haeckel’s definition is one of the 
very best but is too indefinite to be workable. In his conception 
the word species ‘“‘serves as the common designation of all indi- 
vidual animals or plants which are equal in all essential matters 
of form, and are only distinguished by quite subordinate charac- 
ters.” Unsatisfied with the current definitions, I defined species, 
in Survival of the Unlike, as ‘a term used to classify animals 
and plants, by designating or grouping together all those forms 
or individuals which are very much alike in taxonomic marks.” 
But this is too indefinite to be of much use. As I now conceive 
of it, I should define a species as follows: Zhe unit in classtfica- 
tion, designating an assemblage of organisms which, in the Judgment 
a of any writer, is so marked and so homogeneous that it can be conven- 
tently spoken of as one thing. 
Il. Toe Arr or SpEcres-MAKING.—When we come to the 
Practical application and use of the word species, we must admit 
that the more carefully we distinguish the forms of life, the 
_ Smaller or narrower must be the assemblages to which, for rea- 
_ Sons of perspicuity, we apply the word. The smaller the classi- 
ficatory divisions, the more exactly can we speak of organic life. 
We elucidate our subject more by dividing it than we do by 
massing it. I therefore look with favor upon the tendency in 
_ +me quarters to make specific names for forms which have 
_— Retetofore been regarded as well marked varieties, although I 
