in VARIABILITY OF SFECIES IN A STATE OF NATURE 59 
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 dispropor¬ 
tionate. 
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 aloue being given. 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. 
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. These 
fully support the statement of Mr. Allen, since they show an 
equal amount of variability when the numbers compared are 
