PAPILIO IIL, IV., V. 
are common, for a yellow female to produce a black, though the chances are that 
every yellow female in such district has had one or more black female ancestors. 
Therefore, where the black is an extremely rare form, with the chances largely 
against any yellow female having inherited a tendency to melanism, that one 
should produce two black, and two deep ochraceous examples (for this latter col¬ 
oration is of the same nature as the other), is almost as if this variation in the 
present case arose spontaneously. I have applied to several collectors in Brook¬ 
lyn besides Mr. Akhurst, and all agree in the statement that Glaums is an un¬ 
common insect in that vicinity. Mr. Akhurst says also that he has occasionally 
taken such ochraceous individuals in the field. Here at Coalburgh there is ob¬ 
servable in the yellow females a deeper coloring than in the males, especially of 
the fore wings (Plate III., Fig. 1), but I have seen no such example as that from 
Brooklyn. Formerly, in the collection of Mr. Wood, at Philadelphia, 1 saw a 
chocolate colored Glaucus , and Mr. Aaron writes me that he has taken one sim¬ 
ilarly colored. 
Many explanations of the phenomena of melanism in general have been sug¬ 
gested, such as meteorological conditions — excessive moisture, deficient sun¬ 
shine, impure air; also vegetation defiled by soot from furnaces, and the like ; 
none of which are satisfactory when applied to species on this continent, however 
it may be when they are restricted to limited areas, as in parts of Europe. In 
North America, the very reverse of these conditions obtains throughout the re¬ 
gions in which the melanic species are mostly found. And as a rule, melanism 
among butterflies is confined to one sex, and that the female. It is not always 
so, as appears by the melanic Philodice male figured in this volume, but nearly 
every known example belongs to the female. In case of the present species, the 
tacts are, that in the warmer regions, where it is polygoneutic, or many-brooded, 
both yellow and black females exist, in some districts apparently in about equal 
numbers, in others with a more or less decided predominance of the black, but 
occasionally, as in the mountain district visited by Mr. Morrison, the yellow pre¬ 
dominating almost if not quite to the exclusion of the other; that at the north 
the black disappear at the line at which the species becomes monogoneutic, and 
the yellow form in both sexes flourishes even to the arctic portions of the conti¬ 
nent. Dr. W eismann, 1 speaking of Timms, expresses the opinion that “ the yel¬ 
low is the ancient and original form, the black a much younger, or more recent 
lorm.” During the glacial period, when the shortness and coolness of the season 
permitted but one brood in the year, just as in the boreal regions now, the spe¬ 
cies was yellow in both sexes. As the season became longer and climate milder, 
from the receding of the ice which had covered the larger portion of the con- 
1 Ueber den Einfluss der Isolirung auf die Artbildung, Leipzig, 1872, p. 95. 
