54 
DARWINISM 
CHAP. 
There is here no question of “ minute ” or “ infinitesimal ” 
variation, which many people suppose to he the only kind of 
variation that exists. It cannot even he called small; yet 
from all the evidence we now possess it seems to he the 
amount which characterises most of the common species of 
birds. 
It maybe said, however, that these are the extreme variations, 
and only occur in one or two individuals, while the great 
majority exhibit little or no difference. Other diagrams will 
show that this is not the case ; hut even if it were so, it would 
he no objection at all, because these are the extremes among 
thirty specimens only. We may safely assume that these thirty 
specimens, taken by chance, are not, in the case of all these 
species, exceptional lots, and therefore Ave might expect at least 
two similarly varying specimens in each additional thirty. But 
the number of individuals, even in a very rare species, is 
probably thirty thousand or more, and in a common species 
thirty, or even three hundred, millions. Even one individual 
in each thirty, varying to the amount shown in the diagram, 
would give at least a million in the total population of any 
common bird, and among this million many would vary much 
more than the extreme among thirty only. We should thus 
have a vast body of individuals varying to a large extent in 
the length of the wings and tail, and offering ample material 
for the modification of these organs by natural selection. We 
will now proceed to show that other parts of the body vary, 
simultaneously, but independently, to an equal amount. 
The first bird taken is the common Bob-o-link or Rice-bird 
(Dolichonyx oryzivorus), and the Diagram, Fig. 4, exhibits the 
variations of seven important characters in twenty male adult 
specimens. 1 These characters are — the lengths of the body, 
wing, tail, tarsus, middle toe, outer toe, and hind toe, being as 
many as can be conveniently exhibited in one diagram. The 
length of the body is not given by Mr. Allen, but as it forms 
a convenient standard of comparison, it has been obtained by 
deducting the length of the tail from the total length of the 
birds as given by him. The diagram has been constructed 
as follows :—The twenty specimens are first arranged in a 
series according to the body-lengths (which may be con- 
1 See Table I, p. 211, of Allen’s Winter Birds of Florida. 
