PAPILIO III., IV., V. 
So that the black form appears constantly in the spring as well as the summer 
brood. The difference between the summer and winter form of the black female 
in size and ornamentation is well shown in Plates IIP, IV., the first of these 
being the summer. 
From eggs obtained in same way from yellow females, there resulted in the 
spring of 1872, 8 *, 3 *, all yellow. In August, 1875, 3 *, 12 * all yellow, and 
fiom pa 1 1 of the chiysalids of this lot which passed the winter, there appeared in 
the spring of 1876, 4 *, 12 yellow «, 1 black «. This is the only instance out of 
many broods raised, in which a black has come from a yellow mother, though on 
two occasions, besides the one above mentioned, a yellow female has come from 
black. 
Mr. Darwin lays much stress upon the prepotence of transmission, in the case 
of peculiarities transmitted through one sex only of a species, and asserts that 
characters may first appear in either sex and afterwards be transmitted to the 
offspring of the same sex.” « Variation of Animals,” etc., 1st Am. ed., II., p. 106. 
That yellow females should rarely produce black is not surprising, but that 
the reverse should not often and constantly happen, inasmuch as the blacks are 
always crossing with the yellow males, does indicate an amazing energy in the 
black form, and implies a time when the yellow female will wholly succumb to 
the other throughout the regions now inhabited by the two, unless there be in 
certain districts some restraining influence, as climatal, or the existence of ene¬ 
mies. To the northward, and in elevated districts, there must probably be same 
restraining climatal influence on the black form. No black Papilio of any species 
is found in the sub-boreal regions, though on both continents, and at great ele¬ 
vation, the yellow Machaon flourishes, as does Turnus in North America. 
Mi. Wallace, “Natural Selection, p. 154, speaking of Turnus and its dimor¬ 
phism, considers it “ highly probable that the existence of enemies and of com¬ 
peting forms of life, may be the influences which determine the relative propor¬ 
tions of each form ; and hopes that observations may ascertain “ what are the 
adverse causes which are most efficient in keeping down the numbers of each 
of these contrasted forms.” 
In looking for the causes of the decrease of the yellow female in the western 
and southwestern districts, and the manifest luxuriance of the black, it seems to 
me that it is not unlikely largely owing to the facility with which the yellow 
females are captured by birds and other enemies by day. They are slower of 
flight than the males, and when heavy with eggs, are very sluggish, flying but 
little and at short distances, and their gay color renders them an easy prey. It 
is true, the black females are equally slow of flight, but they are less easily seen, 
and as other species of black Papilios, Troilus, Philenor, and A.sterias } are always 
