But
if he confine his attention to one class within one country he will soon
make up his mind how to rank most of the doubtful forms. His general
tendency will be to make many species, for he will become impressed, just
like the pigeon or poultry fancier before alluded to, with the amount of
difference in the forms which he is continually studying; and he has little
general knowledge of analogical variation in other groups and in other
countries by which to correct his first impressions. As he extends the
range of his observations he will meet with more cases of difficulty; for
he will encounter a greater number of closely-allied forms. But if his
observations be widely extended he will in the end generally be able to
make up his own mind; but he will succeed in this at the expense of
admitting much variation, and the truth of this admission will often be
disputed by other naturalists. When he comes to study allied forms brought
from countries not now continuous, in which case he cannot hope to find
intermediate links, he will be compelled to trust almost entirely to
analogy, and his difficulties will rise to a climax.
Certainly no clear line of demarcation has as yet been drawn between
species and sub-species--that is, the forms which in the opinion of some
naturalists come very near to, but do not quite arrive at, the rank of
species; or, again, between sub-species and well-marked varieties, or
between lesser varieties and individual differences.
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