Again, even related parts do not
constantly vary together but present many instances of independent
variation, as shown by the want of parallelism in their respective
variation-lines. In No. 5 (see Fig. 4) the wing is very long, the tail
moderately so; while in No. 6 the wing is much shorter while the tail is
considerably longer. The tarsus presents comparatively little variation;
and although the three toes may be said to vary in general together,
there are many divergencies; thus, in passing from No. 9 to No. 10, the
outer toe becomes longer, while the hind toe becomes considerably
shorter; while in Nos. 3 and 4 the middle toe varies in an opposite way
to the outer and the hind toes.
[Illustration: FIG. 6.--Cardinalis virginianus. 31 Males.]
In the next diagram (Fig. 5) we have the variations in forty males of
the Red-winged Blackbird (Agelaeus phoeniceus), and here we see the same
general features. One-fifth of the whole number of specimens offer a
large amount of variation either below or above the mean; while the
wings, tail, and head vary quite independently of the body.
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