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may here add, that I 1859 1860 1861 1866
OMIT 1869 1872

only briefly give 1859 1860 1861 1866
only give 1869
give only 1872

several of the 1859 1860 1861 1866
the same 1869 1872

differ 1859 1860 1861 1866 1869
of the same species differ 1872

of 1859 1860 1861 1866
belonging to 1869
belonging to other 1872

birds within 1859 1860 1861 1866 1869
with birds the individuals of 1872

country vary in a remarkably small degree, 1859 1860 1861 1866
country vary in a remark- ably small degree, 1869
species, inhabiting the same country, vary extremely little, 1872

seems to me certainly 1859 1860 1861 1866 1869
certainly seems 1872

more
more
rarely
rarely
to
to
them.
them.
The rule being so plainly applicable in the case of secondary sexual characters, may be due to the great variability of these characters, whether or not displayed in any unusual
manner —
manner—
of which fact I think there can be little doubt. But that our rule is not confined to secondary sexual characters is clearly shown in the case of hermaphrodite cirripedes;
and
and
I may here add, that I particularly attended to Mr.
Waterhouses
Waterhouse's
remark, whilst investigating this Order, and I am fully convinced that the rule almost
always
invariably
holds
good.
good
with
with
cirripedes.
cirripedes.
I shall, in
a
my
future work, give a list of
all the
the
more remarkable cases; I will here only briefly give one, as it illustrates the rule in its largest application. The opercular valves of sessile cirripedes (rock barnacles) are, in every sense of the word, very important structures, and they differ extremely little even in
distinct
different
genera; but in the several species of one genus, Pyrgoma, these valves present a marvellous amount of
diversification;
diversification:
the homologous valves in the different species being sometimes wholly unlike in shape; and the amount of variation in the individuals of several of the species is so great, that it is no exaggeration to state that the varieties differ more from each other in the characters
derived from
of
these important
organs,
valves
than do
the
other
species of distinct genera.
As birds within the same country vary in a remarkably small degree, I have particularly attended to
them;
them,
and the rule seems to me certainly to hold good in this class. I cannot make out that it applies to plants, and this would
have seriously
seriously have
shaken my belief in its truth, had not the great variability in plants made it particularly difficult to compare their relative degrees of variability.
When we see any part or organ developed in a remarkable degree or manner in
a
any
species, the fair