The extreme divergence of each of the lines in a vertical direction
shows the actual amount of variation; and if we consider the small
length of the toes of these small birds, averaging about three-quarters
of an inch, we shall see that the variation is really very large; while
the diverging curves and angles show that each part varies, to a great
extent, independently. It is evident that if we compared some thousands
of individuals instead of only twenty, we should have an amount of
independent variation occurring each year which would enable almost any
modification of these important organs to be rapidly effected.
[Illustration: FIG. 7.--Variation of Tarsus and Toes.]
[Illustration: FIG. 8.--Variation of Birds in Leyden Museum.]
In order to meet the objection that the large amount of variability here
shown depends chiefly on the observations of one person and on the birds
of a single country, I have examined Professor Schlegel's Catalogue of
the Birds in the Leyden Museum, in which he usually gives the range of
variation of the specimens in the museum (which are commonly less than a
dozen and rarely over twenty) as regards some of their more important
dimensions.
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