The wing and
tail too, though showing some amount of correlated variation, yet in
no less than nine cases vary in opposite directions as compared with the
preceding species.
The next diagram (Fig. 6), showing the variations of thirty-one males of
the Cardinal bird (Cardinalis virginianus), exhibits these features much
more strongly. The amount of variation in proportion to the size of the
bird is very much greater; while the variations of the wing and tail not
only have no correspondence with that of the body but very little with
each other. In no less than twelve or thirteen instances they vary in
opposite directions, while even where they correspond in direction the
amount of the variation is often very disproportionate.
As the proportions of the tarsi and toes of birds have great influence
on their mode of life and habits and are often used as specific or even
generic characters, I have prepared a diagram (Fig. 7) to show the
variation in these parts only, among twenty specimens of each of four
species of birds, four or five of the most variable alone being given.
Pages:
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124