862 The American Naturalist. [October, 
their present characteristics. On the one side I see variations which 
have become sufficiently fixed to be considered specific; yet which can 
have no especial bearing on the life necessities of the species, but are 
a consequence rather of that universal tendency to variation with 
which every student of Nature becomes profoundly impressed. Thus 
the wing-markings vary from a darker general coloring, as in 
Prodoxus cnescens, to a more uniform intermixture of the black 
scales among the white, as in cinereus, or a sparser intermixture 
thereof, as in pulverulentus. The disposition of the black scales is in 
spots or bands, whether transverse or longitudinal, as in marginatus, 
reticulatus, Y-inversus, etc. These are fortuitous variations, for I can- 
cannot believe that the disposition of these marks where, as in these 
cases, they take every form that is conceivable, can be of any benefit 
to the species, any more than the mere variation in the number of 
lobes in the leaves of different oaks growing under like conditions can 
be of any particular benefit to the species, however useful to us in 
classification. 
“In my address before the Section of Biology of the American 
Association for the Advancement of Science, at Cleveland, in 1888, I 
have discussed the various forms and causes of variation, and 
especially the limitations of natural selection, stating expressly that 
this last “deals only with variations useful to the organism in its 
-struggle for existence, and can exert no power in fixing the endless 
number of what, from present knowledge, we are obliged to consider 
fortuitous characters,” and I have long recognized, from my studies of 
insect life, the existence of these fortuitous variations. The subject 
-has since been very well elaborated by Professor Ward in his com- 
munication to the Society (December 15, 1888) on “ Fortuitous varia- 
tion as illustrated by the genus Eupatorium” and in his Annual 
Address (January 24, 1891) on “ Neo-Darwinism and Neo-Lamarck- 
ism,” and the Prodoxide furnish an excellent illustration of this 
fortuitous variation. Yet at the same time that we note this chance 
variation, as exemplified in a number of the species of Prodoxus, 
which are mere ravagers or despoilers and have not been brought into 
any special or mutual relations with the plant, we have, on the other 
hand, in Pronuba yuceasella, correlated with the other striking 
structural modifications whjch have brought it into such special rela- 
-tions with the plant, an elimination of all maculation or markings 
upon the primaries, and a purely white coloring so fixed that it shows 
absolutely no variation over half the continent. The structural 
variation has been necessary—a consequence of effort, environment, 
