24 Experimental Zoology 
temperature a lighter one, this is not invariably the rule, 
as seen in certain dimorphic forms. Thus, in Lythria rotaria 
the butterfly that hatches in the spring (from over-wintering 
pupe) is darker than the summer type (the second generation, 
variety L. purpuraria). On the other hand, Vanessa levana 
(also from over-wintering pup) is /ighter than the summer 
variety, V. prorsa. A lower temperature does not therefore 
always produce darker colors and a higher temperature lighter 
ones, although this is the general rule, but the reaction depends 
also on the nature of the organism. 
In these experiments with butterflies the more conspicuous 
result is the change in color; but it should not be forgotten that 
changes in size also often occur, and even constant changes in the 
shape of the wings have been observed, the outline of the wing in 
some cases being quite different from that of the normal animal. 
Effect of Temperature on Cater pillars 
Standfuss has shown that by rearing caterpillars at a higher 
temperature (20°-25° C.) than normal, the characters of the 
moths may be affected.'. Changes in the shape of the wings 
are sometimes caused in this way. The color is also altered 
to some extent. The most constant change, however, is in 
the size. Standfuss gives the following rule: “The more 
the feeding period of the caterpillar is shortened by raising the 
temperature the smaller the butterflies. Lasiocampa quercifolia, 
for example, had its weight decreased in this way to one 
seventh of the normal. On the other hand, if the time of feed- 
ing (or in other words the time of the caterpillar stage) is not, 
or only very slightly, shortened, despite the higher temperature, 
there is an increase in size, which in the case of Arctia fasceata 
may be as much as half again the entire normal weight.” 
Standfuss points out that results similar to these are found 
in nature where the size of certain forms appears to be connected 
with the time of year at which the pupe appear. Species 
* Merrifield also has made observation on the effects of temperature on 
caterpillars. 
