JAN. 1907. 
THE ORIGIN OF SPECIES. 
13 
pigment along the shaft, beginning at the apex of the feather and 
advancing gradually inward. The old Turtle-Dove character thus 
passes by a continuous process of division into the Rock Pigeon 
pattern, consisting of two checkers on each feather, more or less 
completely separated. The evidences showing such a gradual trans- 
mutation are still to be seen, and in such profusion as to wholly 
exclude doubt. Hundreds of species have been formed in this 
simple way, leaving no room for the claim of sudden, non-transi- 
tional mutations. 
The transitional stages between the Turtle-dove pattern and 
the checkered pattern of the Rock pigeons, are exhibited not only 
as we pass from one species to another, but often as we advance 
from the juvenal to the adult plumage ; and frequently they may 
be seen in different parts of one and the same individual plumage. 
A still older character than the Turtle-dove spot is seen in the 
cross-bars, or fundamental bars, that appear to mark all feathers 
of all species of birds. These bars were first noticed in pigeons 
in the summer of 1903, and were soon found to be common to all 
species of pigeons and birds in general. From these fundamental 
feather-bars or their secondary derivatives, a multitude of specific 
characters have been evolved by gradual modification. The con- 
tinuity in the evolution of some of these characters can be experi- 
mentally demonstrated. The little Diamond Dove (Geopelia 
cuneata) of Australia, owes its small white spots (two in each 
feather) to these bars. The transitional stages connect- 
ing the spots with the bars are not wholly given in pas- 
sing from the juvenal to the adult plumage. But if we 
pluck a few of the juvenal feathers at suitable intervals, their 
places will be filled by new feathers of different ages, and in this 
way we may get the stages intermediate between the bars of the 
yonng and the spots of the adult. Thus we see that the adult 
pattern, zvhich normally appears to come in as a striking mutation, 
by a single jump, is only an end-stage in a continuous process of 
differentiation. So it is everywhere. Suppression of stages in 
ontogeny looks like saltations ; but whenever we can get at the 
history of the character, we find the continuity comes to light. 
The characteristic secondary cross-bars of many races of the 
common fowl, pheasants, Guinea-fowl, ducks, woodpeckers, etc., 
have been moulded more or less directly out of, or upon these fun- 
