264 MONTGOMERY. [Vo. XII. 
ably still under the agency of a process of development. But 
though this reasoning may be plausible, it is based upon Wal- 
lace’s assumption that the production of such characters is due 
to the agency of the sexual impulse ; and rather than bind myself 
to such a theory, I would leave the case still disputable, whether 
or no the presence of noticeable secondary sexual characters 
should be taken as a criterion of continuing development. 
IB: Data. 
It now remains to produce data in support of the thesis 
that individual variation is always concomitant with continu. 
ing development ; and to do this, it must be demonstrated 
successively that (1) variation is always predominant in those 
domestic animals which have been most carefully selected by 
man; (2) in such species as are divisible into geographical 
races; and (3) in those species which undertake extensive 
periodical migrations. 
Variation in domesticated animals is very marked, and espec- 
ially so in those forms which have been most carefully selected 
by man. It is of interest to compare the diversity of breeds 
of the dog with the fewer breeds of the cat ; the former is of 
greater practical use than the latter, and man has subjected it 
consequently to a greater diversity of conditions of life. Whether 
a greater amount of individual variation is evinced by the 
domesticated animals than by their allies in a state of nature, 
cannot as yet be answered with certainty, since, as Bateson 
(/.c.) observes, the phenomena of variation in the wild forms are 
not known to the same extent. Cope (‘ Origin of the Fittest ’’) 
mentions the peacock and the Guinea fowl as forms which have 
not been rendered variable by domestication; but these two 
may be classed as the wildest, and least carefully bred by human 
selection, of any of the domesticated birds. However, without 
coing further into the much-discussed question of variation 
under domestication, the fact is sufficient for us that animals 
show considerable individual variation under domestication, 
and that the amount of variation is greatest in those species 
which have been most influenced by human selection; and we 
