40 i REVIEWS. 
other way will their true character be more likely to be eventually 
made evident; for those authors who have recognized them as — 
valid will be likely to reinvestigate the subject before submitting — 
to their being dropped from our systems. All zoologists, I think, 
will admit that the tendency is to a multiplication of nominal 
species; and all likewise know how difficult it is to eradicate a 
nominal species from our systems. Probably few naturalists now — 
doubt that many currently received species rest solely on char- 
acters of individual variation, and it seems to me unwise to retain 
such species as are unquestionably of this character in the hope that 
through some fortunate circumstance they may be some day proved 
valid. It séems to me impossible, in fact, that any one who has 
compared a large number of specimens of any well known species 
with each other, can resist the conviction that, as the number of — 
specimens in our museums increases, the number of species will 
be greatly reduced, notwithstanding that in the mean time nota 
few really new ones may be discovered. I have myself found that — 
the more common species of both the birds and mammals of east- — 
ern North America—of which I have examined, in many instances, 
hundreds of specimens of each—vary in size, and even in propor- — 
tions, in specimens from the same locality and of the same sex, — 
from twelve to twenty per cent. of their average size and form for 
that locality, and to a corresponding extent in color. Add to this 
the: ortun range of the geographical variation each species €x- — 
hibits, which ordinarily fully equals that of the individual varia- 
tion, * and it becomes at once evident that with the custom of — 
zoologists to describe species from a single specimen, and often 
an imperfect one, and their usual want of familiarity with the ex- 
tent of variation within specific limits in the common species of 
their own country, the liabilities to an undue multiplication of 
species have been, and still are, very great. This to many may be — 
3 matter of small moment, but to the philosophical zoologist, who - 
esires to carefully Investigate the varied phenomena of animal : 
life, it is one of high importance, 
pei: said thus much in reply to the strictures of Dr. Gill, I 
now reluctantly turn critic, and pass in review the classification of 
‘ = 
See on this subject a paper in the Bulletin of the Museum of Comparative Zoology ; 
and Geographical Variation among — 
e Value of Certain Assu 
- (Vol. I, pp. 186-250) entitled, “ On 
. i k 
Birds, considered in Respect to its ton ayie man 
Characters,” 5 
D MPE u 
REEE in iin 
AT es 
Y 
