28 
Psyche 
[March 
ON CERTAIN FORMS OF COMMON AMERICAN 
BUTTERFLIES. 
By Austin H. Clark 
Smithsonian Institution, Washington, D. C. 
In any large series of butterflies of any single species the 
individuals are seen to be divisible into various forms. These 
forms are of two types, those due to a response to environ- 
mental conditions, that is, to a response to the chemistry 
and physics of their environment, and those due to physio- 
logical indiosyncracies on the part of certain individuals, 
that is, to their internal chemical and physical condition. 
Examples of the first are cold and hot and wet and dry 
forms and local varieties. Examples of the second are alter- 
native forms in either sex or in both sexes, and most of 
the variants usually classed as “aberrations.” 
There is no sharp distinction between these two classes, 
for a species may have, for instance, a long range of alter- 
native forms in one region and none in another, or variants 
of one or several types may be frequent in one area and rare 
or unknown elsewhere, or may occur only in certain years, 
which clearly has to do with environment. 
In the following pages attention is called to a few forms 
from among our common native butterflies which, by ana- 
logy with corresponding forms elsewhere, seem susceptible 
of interpretation as wet and dry forms. 
It is presumable that a wet form of a butterfly is a form 
adapted to developing in the presence of an amount of mois- 
ture equalling or in excess of the maximum requirements. 
This moisture may be furnished either in the form of abun- 
dant water in the food, or abundant water available for 
ingestion with the food. A dry form would be a form living 
in the younger stages on food with an amount of water at or 
near the minimum requirements. This might be due (1) to 
seasonal variation in the precipitation, (2) to differences in 
soil conditions, as between bogs and well drained dry up- 
lands, or to seasonal variation in the condition of the food 
