such characters are exceedingly common. Mr. Romanes says that,
upon his theory of physiological selection, "it is quite intelligible
that when a varietal form is differentiated from its parent form by the
bar of sterility, any little meaningless peculiarities of structure or
of instinct _should at first be allowed to arise_, and that they should
then _be allowed to perpetuate themselves_ by heredity," until they are
finally eliminated by disuse. But this is entirely begging the
question. Do meaningless peculiarities, which we admit often arise as
spontaneous variations, ever perpetuate themselves in all the
individuals constituting a variety or race, without selection either
human or natural? Such characters present themselves as unstable
variations, and as such they remain, unless preserved and accumulated by
selection; and they can therefore never become "specific" characters
unless they are strictly correlated with some useful and important
peculiarities.

As bearing upon this question we may refer to what is termed Delboeuf's
law, which has been thus briefly stated by Mr. Murphy in his work on
_Habit and Intelligence_, p. 241.

"If, in any species, a number of individuals, bearing a ratio
not infinitely small to the entire number of births, are in
every generation born with a particular variation which is
neither beneficial nor injurious, and if it is not counteracted
by reversion, then the proportion of the new variety to the
original form will increase till it approaches indefinitely near
to equality."

It is not impossible that some definite varieties, such as the melanic
form of the jaguar and the bridled variety of the guillemot are due to
this cause; but from their very nature such varieties are unstable, and
are continually reproduced in varying proportions from the parent forms.
They can, therefore, never constitute species unless the variation in
question becomes beneficial, when it will be fixed by natural selection.
Darwin, it is true, says--"There can be little doubt that the tendency
to vary in the same manner has often been so strong that all the
individuals of the same species have been similarly modified without the
aid of any form of selection."[46] But no proof whatever is offered of
this statement, and it is so entirely opposed to all we know of the
facts of variation as given by Darwin himself, that the important word
"all" is probably an oversight.

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