The Influence of External Conditions a7 
The Influence of Light, Electricity, Centrijugal Force, Chemical 
Substances, and Oxygen on the Caterpillars and Pupe of 
Moths and Butterflies 
It has been shown by Grdfin von Linden that the size, the 
colors, and the markings of butterflies may be altered by sub- 
jecting the caterpillars or the pupe to several kinds of external 
conditions other than temperature. In general, however, the 
results are similar to the effects produced by higher and lower 
temperatures. 
Light. — Vanessa urtice and V. io were used. Some of 
the caterpillars were kept, with their food, in red, or green, or 
blue light. Others were kept in the dark. The principal 
changes were in the ground color of the wings of the butterflies. 
This was intensest and brightest in red light, dusky in green, 
and paler in blue and in the dark. The butterflies of V. urtice 
were largest from the caterpillars reared in the blue, and of V. 
io in the dark. The changes in the markings were very slight. 
Electric Shocks. — The pupe of V. urtice, in a fresh but dry 
condition, were put into an iron box through which an electric 
current was passed of sufficient strength to cause a pricking 
sensation when applied to the hand. In other cases one elec- 
trode was applied at the wing axis and the other at the tip of 
the wing case. The resulting butterflies were brightly colored. 
The black border of the wing was broader, and the tip of the 
wing was sometimes dark. The blue and yellow scales of the 
sides of the wing were little developed. 
Centrifuge, — After the pupe had become hard they were 
subjected to a centrifugal force for ten minutes each day. The 
effects were in general similar to those caused by light. 
Chemical Substances. — Contrary to the results of Standfuss, 
who found changes in the food had no influence on the color 
of the moth, except in one case, when salt was added to the food 
of Callema, Grafin von Linden found that certain substances 
given with the food produced distinct effects. Some effects, for 
the most part slight, were obtained with (1) defibrinated blood ; 
