considerations to be given throughout this work.

It need not be supposed that all varieties or incipient species attain the
rank of species. They may become extinct, or they may endure as varieties
for very long periods, as has been shown to be the case by Mr. Wollaston
with the varieties of certain fossil land-shells in Madeira, and with
plants by Gaston de Saporta. If a variety were to flourish so as to exceed
in numbers the parent species, it would then rank as the species, and the
species as the variety; or it might come to supplant and exterminate the
parent species; or both might co-exist, and both rank as independent
species. But we shall hereafter return to this subject.

>From these remarks it will be seen that I look at the term species as one
arbitrarily given, for the sake of convenience, to a set of individuals
closely resembling each other, and that it does not essentially differ from
the term variety, which is given to less distinct and more fluctuating
forms. The term variety, again, in comparison with mere individual
differences, is also applied arbitrarily, for convenience sake.

WIDE-RANGING, MUCH DIFFUSED, AND COMMON SPECIES VARY MOST.

Guided by theoretical considerations, I thought that some interesting
results might be obtained in regard to the nature and relations of the
species which vary most, by tabulating all the varieties in several
well-worked floras. At first this seemed a simple task; but Mr. H.C.
Watson, to whom I am much indebted for valuable advice and assistance on
this subject, soon convinced me that there were many difficulties, as did
subsequently Dr. Hooker, even in stronger terms. I shall reserve for a
future work the discussion of these difficulties, and the tables of the
proportional numbers of the varying species. Dr. Hooker permits me to add