Ill 
VARIABILITY OF SPECIES IN A STATE OF NATURE 57 
sidered 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. In this case (and 
wherever practicable) the body-length is measured from the 
lower line of the diagram, so that the actual length of the bird 
is exhibited as well as the actual variations of length. These 
can be well estimated by means of the horizontal line drawn 
at the mean between the two extremes, and it will be seen 
that one-fifth of the total number of specimens taken on either 
side exhibits a very large amount of variation, which would of 
course be very much greater if a hundred or more specimens 
were compared. The lengths of the wing, tail, and other parts 
are then laid down, and the diagram thus exhibits at a glance 
the comparative variation of these parts in every specimen as 
well as the actual amount of variation in the twenty specimens; 
and we are thus enabled to arrive at some important con¬ 
clusions. 
We note, first, that the variations of none of the parts follow 
the variations of the body, but are sometimes almost in an 
opposite direction. Thus the longest wing corresponds to a 
rather small body, the longest tail to a medium body, while 
the longest leg and toes belong to only a moderately large body. 
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. 
In the next diagram (Fig. 5) we have the variations in 
forty males of the Red-winged Blackbird (Agelteus phceniceus), 
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. The wing and tail too, 
