We will now proceed to show that other
parts of the body vary, simultaneously, but independently, to an equal
amount.
[Illustration: FIG. 4.--Dolichonyx oryzivorus. 20 Males.]
[Illustration: FIG. 5.--Agelaeus phoeniceus. 40 Males.]
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.[21] 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 considered to give the size of the bird), from the
shortest to the longest, and the same number of vertical lines are
drawn, numbered from one to twenty.
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