INTRODUCTION 73 
living individuals, he soon perceives that the divisions 
are much less abrupt than he had supposed. He finds 
that the changes of type are gradual and almost insensi- 
ble, and that some of the forms that had appeared to 
him definite and fixed, blend by degrees with others 
which he had considered to be distinct. He necessarily 
abandons many of his preconceived views as to spe- 
cific distinctions, and is obliged to modify all of them 
more or less by his new experience. Every naturalist 
should therefore test his opinions by an intimate ac- 
quaintance with living species existing in their natural 
conditions. It is true that but few of our naturalists 
could heretofore comply with these preliminary requisi- 
tions, and perhaps the most complete collections in the 
country, public or private, have not been sufficiently 
ample to afford the means of making so thorough a 
comparison as we consider to be necessary ; yet the 
rules we lay down are good ones, and, if observed so 
far as circumstances will permit, will be of great ser- 
vice to science. If our naturalists had been guided 
by them during the short career of American zoology. 
we should now be free from an amount of error in re- 
spect to our own species, which, in the period of twenty- 
five years, has created a synonymy wellnigh as con- 
fused as that wliich in Europe has been accumulating 
more than twice that length of time. The excuse for 
error which formerly existed, in the want of means for 
learning what is correct, can no longer be received, for 
the facilities arising from ample collections of shelh and 
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