8 
JOURNAL OP MAMMALOGY 
In the case of errors resulting from inadequate material — the hover- 
ing demon of the systematic worker — no prophylactic treatment has 
yet been discovered, though experience and judgment count for much in 
lessening the frequency and severity of incorrect conclusions. 
The history of the progress of ornithology and mammalogy in 
America proves that by the criterion of intergradation many forms 
have been described as subspecies that later proved to be either inde- 
pendent species or offshoots of species other than those to which they 
were originally referred, showing that it is the 'practice of naturalists to 
ASSUME inter gradation rather than prove it. The truth of this may be 
demonstrated ‘ by an examination of the published records of speci- 
mens examined, for while actual intergrades are often at hand, the 
record shows that in the great majority of cases the author did not see 
specimens from intermediate localities — the only localities from which 
intergrades could possibly have come. 
W. H. Osgood, in his monographic Revision of the Mice of the American 
genus Peromyscus, had before him the unparalleled collections of the 
United States Biological Survey, supplemented by those of various 
museums and individuals, amounting in all to upwards of 27,000 
specimens. In studying this astounding wealth of material, cover- 
ing practically all parts of the North American continent, he natu- 
rally found a large number of intergrades, in connection with which 
circumstance he says: “Until recent years continuous and perfect 
intergradation was demonstrable only in relatively few cases. And 
even now, although proved beyond doubt in group after group, in 
many cases it is merely taken for granted.’’ (N. Am. Fauna No. 28, 
p. 17, April, 1909.) 
More than twenty years ago, after serving for a number of years as a 
member of the A. 0. U. Committee on Nomenclature and Classifica- 
tion of North American Birds, I was so impressed by the inconsisten- 
cies, shiftings of rank, and illogical conclusions necessitated by the 
intergradation rule that I published in Science the following protest 
and suggestion: 
In practice it has been found that only in a small percentage of cases does 
an author have at his command a sufficiently large series of specimens, from a 
sufficient number of well-selected localities, to enable him to say positively 
that related forms do or do not intergrade. The result of this obvious embarrass- 
ment is that authors usually exercise their individual judgment as to the prob- 
able existence or non-existence of intergradation, thus introducing the personal 
equation it was hoped to avoid It would seem therefore .... 
