4 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 see'ms to me unwise to retain 

 such species as are unquestionably of this character in the hope that 

 through some fortunate circumstance they may be spme day proved 

 valid. It seems 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 not a 

 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 localit}^ and of the same sex, 

 from twelve to twent}^ per cent, of their average size and form for 

 that locality, and to a corresponding extent in color. Add to this 

 the normal range of the geographical variation each species ex- 

 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 

 a matter of small moment, but to the philosophical zoologist, who 

 desires to carefully investigate the varied phenomena of animal 

 life, it is one of high importance. 



Having 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 tharMuseum of Comparative Zoology 

 (Vol. II, pp. 186-250) entitled, "On the Individual and Geographical Variation among 

 Birds, considered in Respect to its Bearing upon the Value of Certain Assumed Specific 

 Characters." 



