PAPILIO III., IV., V. 
tinent, there was at length time for a second brood to mature the same season, 
and the species gradually became digoneutic. Still later, for the same reasons, 
in the more southern districts, a third generation could mature. And with the 
summer generation, at some stage, came in the black form, which is restricted 
even now to the districts in which a summer generation is possible. The cause 
may have been in some way climatal, or this variety may at first have been 
accidental, and once in existence, favored by circumstances, was able to perpet¬ 
uate its type through its descendants till it has become common, sometimes almost 
to the exclusion of the yellow and original form. 
“ The origin of the black form we can only explain by supposing that, at one 
time, when Turnus already occupied a territory as extensive as it holds to-day, 
some unknown influence caused the black female form to appear as a distinct 
variety, and that, owing to some circumstance, it thereby gained an advantage 
over its rival, which caused it finally to supplant the other, and to spread over a 
large extent of country. This supplanting process must have begun with one 
individual, or a very few individuals. There is no case known where a whole 
species became aberrant, and the supposition that the black form appeared sim¬ 
ultaneously among hundreds or thousands of individuals may be rejected as 
untenable.One or a few black females, here stand opposed to myriads 
of yellow ones, and have finally proved victorious over them.This vic¬ 
tory can be explained in no other way than through the supposition of the use¬ 
fulness of the black color.” Dr. Weismann inclines to consider it a case of sexual 
selection, the superiority of the blacks having been gained by their attractiveness 
to the males. However this may be in general, it may be stated that the yellow 
females taken by me, at Coalburgh, have as surely been fertilized as the blacks, 
and have as readily laid eggs ; and on the wing the males may be seen coquet¬ 
ting with the yellow as freely as with the blacks. There would seem to be no 
want of attractiveness in such individual instances. 
I have experimented to see if it were possible that the butterflies emerging 
from chrysalis in midsummer might show a stronger tendency to melanism than 
those emerging in the spring, from over-wintering chrysalids, but have found no 
evidence that the heat of summer or cold of winter exert influence on the re¬ 
sulting forms of the female. In June, 1875, T obtained eggs by confining several 
black females upon the limbs of a tulip tree, and there resulted therefrom, in Au¬ 
gust following, 9 <*, 2 black ? . Part of the chrysalids passed the winter, and in 
the spring there emerged 9 d , 5 black ? . 
In the spring of 1872, there emerged from chrysalids of the previous year, the 
eggs having been laid by black females, 15 *, 7 black ? , 2 yellow ? . 
In the spring of 1877, from eggs laid by black, 21 7 black 
