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Transactions of the Society. 
often no more than a matter of individual taste.” * They thus re- 
nounce the belief “ that species are ‘ definite entities/ differing in kind 
from ‘ varieties’ on the one hand and from genera ’ on the other.” 
The obvious consequence of such views was expressed in a paper 
communicated to the Zoological Society in 1880 by Prof. Huxley : 
“ As for species, no one zoologist has ever yet agreed with the 
estimate of another as to what should be considered species and what 
local varieties among wolves and foxes ; and as there is no criterion 
by which the question can be tested, it is probable that such agree- 
ment never will be attained. The suggestion that it may be as well 
to give up the attempt to define species, and to content oneself with 
regarding the varieties of pelage and stature which accompany a 
definite type of skeletal and dental character in the geographical 
district in which the latter is indigenous, may be regarded as revolu- 
tionary, but I am inclined to think that sooner or later we shall have 
to adopt it.” t 
In the presence of such authorities it is necessary to speak with 
the greatest respect and the utmost possible caution ; but I would 
ask, does it follow “ as a necessary deduction from the theory of de- 
scent ” that species are thus “ merely arbitrary divisions ” ? Is it not 
open, even to those who accept unreservedly the theory of evolution, 
and have not the slightest vestigial belief that “ such divinity doth 
still hedge in a species,” to regard them as having some real existence 
in Nature ? 
As regards genera, families, orders, &c. there is nothing to be said. 
They may be granted to be purely conventional terms, adopted for 
convenience of classification, for the ready indication of natural affinity, 
and for facility of memory. For such purposes they are of use, with- 
out any question of their existence in Nature. 
A “ species/ ’^on the contrary, appears to me to be still possibly not 
a mere term, an idea, an arbitrary division for the convenience and 
assistance of naturalists, but to possess a real existence in Nature, in- 
asmuch as it is marked by a clear distinction from the varieties out of 
which it originally sprang. Whether the distinction be one of “ kind ” 
or merely of degree, is of no consequence, so long as it suffices to render 
the species physiologically distinct, and thereby to constitute it an 
“ organic unit.” 
This distinction, I venture to suggest, lies in the degree of differ- 
entiation of the sexual elements, or of those elements which in con- 
jugation coalesce to perform the reproductive function, however little 
we may know of the nature or of the cause of such differentiation. 
Mr. Darwin, summing up the results of his experiments on 4 The 
Cross- and Self-fertilisation of Plants/ i writes, “ It is an extra- 
ordinary fact that, while many species of flowers fertilised with their 
own pollen are either absolutely or in some degree sterile ; if fertilised 
* Tom. cit., p. 254. f Proc. Zool. Soc., 1880, p. 286. X P- 455. 
