ILLUSTRATIVE OF NATURAL SELECTION, 165 
tribution of Arctic Plants,” (Trans. Linn. Soc. xxiii., 
p. 810) Dr. Hooker says:—“The most able and ex- 
perienced descriptive botanists vary in their estimate 
of the value of the ‘specific term’ to a much greater 
extent than is generally supposed.” . . ‘I think 
I may safely affirm that the ‘specific term’ has three 
different standard values, all current in descriptive 
_ botany, but each more or less confined to one class 
of observers.” . . ‘This is no question of what 
is right or wrong as to the real value of the spe- 
cific term; I believe each is right according to the 
standard he assumes as the specific.” 
Lastly, I will adduce Mr. Bates’s researches on the 
Amazons. During eleven years he accumulated vast 
materials, and carefully studied the variation and dis- 
tribution of insects. Yet he has shown that many 
species of Lepidoptera, which before offered no special 
difficulties, are in reality most intricately combined 
in a tangled web of affinities, leading by such gradual 
steps from the slightest and least stable variations to 
tixed races and well-marked species, that it is very 
often impossible to draw those sharp dividing-lines 
which it is supposed that a careful study and full 
materials will always enable us to do. 
These few examples show, I think, that in every 
department of nature there occur instances of the in- 
stability of specific form, which the increase of mate-_ 
rials aggravates rather than diminishes. And it must 
be remembered that the naturalist is rarely likely to 
err on the side of imputing greater indefiniteness to 
