CHAPTER III 
THE INFLUENCE OF EXTERNAL CONDITIONS IN CAUSING 
CHANGES IN THE STRUCTURE OF ANIMALS (Continued) 
Experiments on the Influence of the Food Plant 
PicTET has studied the influence of the food of the caterpillar 
on the color, the size, and other characters of the butterfly. 
As a rule the caterpillars of each species are found on a par- 
ticular plant, and cannot be induced to eat the leaves of a differ- 
ent one, or only with great difficulty. A few species, however, 
are polyphagous, 7.e. they feed on a number of different plants. 
For example, the caterpillars of the Arctiidae feed upon all sorts 
of herbaceous plants; many Noctuidae consume indifferently 
several species of Composite; Papilio macchaon lives on dif- 
ferent Umbellifere; Ocneria dispar, Porthesia chrysorrhea, and 
Bombyx neustria are found on nearly all kinds of trees. Occa- 
sionally caterpillars are found on plants that are not those nor- 
mal for them, and the question has often been asked whether 
the aberrant types of butterflies sometimes met with may not 
have arisen in consequence of a change in the food plant. This 
question Pictet has studied experimentally. 
In captivity certain caterpillars adapt themselves readily to 
very different kinds of food. As a rule a caterpillar will feed 
on the flowers of its natural plant, and even the fruit may be 
used, as in the case of Cossus cossus, which will eat pieces of 
apple instead of the wood and the bark of the tree. 
It appears that in nature, also, certain species have recently 
extended their dietary. Thus Lasiocampa quercus was known 
at the time of Linneus to feed on the oak tree (as its 
1 These examples are given by Pictet. 
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