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BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 5, NO. 1. 
as many allied species as possible, and endeavor to get the past 
history of the character. To experiments in breeding we must add 
those of crossing, as in this way we can best see whether a char- 
acter is an indivisible unit, that admits of no transmutation by con- 
tinuous modification. It is by such study that we may arrive at 
most important laws of heredity. In fact we study the origin of 
species, not as a curiosity, but as a practical problem, the solution 
of which must contribute eventually to human progress. 
With these introductory remarks, the lecturer turned to the 
consideration of a few specific characters which are found in vari- 
ous species of pigeons. 
The wing-bars found in domestic races and in the wild .Rock 
Pigeons, were taken as an example to illustrate orthogenetic evo- 
lution by gradual progressive modification. It was shown first of 
all that the tzvo-harred condition seen in the typical Cohimba livia 
is derived from the checkered condition seen in the wild C. afUnis. 
It was then shown that this mode of derivation is wide-spread 
among wild species of pigeons, the bars always resulting from a 
reduction of the checkers, proceeding from before backward, the 
direction being the same as that of embryonic development. 
Experiments with domestic pigeons demonstrate that it is easy 
to reduce the checkered type to four bars, then to three, two, one, 
and finally, to a uniform gray color without a single bar. Another 
set of experiments, to test the possibility of reversing the process, 
by advancing from the two-barred condition to the uniformly 
checkered type, showed that the direction could not be reversed. 
It was next shown that among wild species of pigeons, we have 
the same law of orthogenesis illustrated over and over again, in 
almost endless variety of conditions. The Wild Passenger Pigeon, 
the Mourning Dove, the Zenaida, the Ground Dove of Florida, 
and a number of Old World species, were shown in colored draw- 
ings on charts. 
After tracing wing-bars of the most diverse kinds to checkers, 
the origin of the latter from a still earlier and universal avian 
character, was explained. This earlier color-mark still persists in 
many pigeons, and other avian types, and is well preserved in the 
oriental Turtle Dove of Japan and China. 
It consists of a single dark spot occupying the centre of the 
exposed part of each feather. In the course of evolution, this spot 
has been divided into two lateral spots by the disappearance of 
