The Origin of the Markings of Caterpillars. 313 



on which it lives. If it is a small caterpillar, i.e., 

 if its length and thickness do not considerably 

 exceed that of the parts of its food-plant, it 

 can scarcely be better concealed stripes would 

 hardly confer any special advantage unless the 

 parts of the plant were also striped. But the case 

 is quite different if the caterpillar is considerably 

 larger than the parts of the plant (leaves, stalks, 

 &c.). The most perfect adaptive colouring would 

 not now prevent it from standing out con- 

 spicuously as a larger body, among the surround- 

 ing parts of the plants. It must be distinctly ad- 

 vantageous therefore to such a caterpillar to be 

 striped, since these markings to a certain extent 

 divide the large body into several longitudinal 

 portions they no longer permit it to be seen as 

 a whole, and thus act more effectively than mere 

 assimilative colouring in causing it to escape detec- 

 tion. This protection would be the more effica- 

 cious if the stripes resembled the parts of the plant 

 in colour and size, such, for instance, as the lines 

 of light and shadow produced by stalks or by long 

 and sharp-edged leaves, 



If this view be correct, we should expect longi- 

 tudinal stripes to be absent in the smallest cater- 

 pillars, and to be present more especially in those 

 species which live on plants with their parts 

 similarly disposed, i. e., on plants with numerous 

 thin, closely-growing stalks and grass-like leaves, 

 or on plants with needle-shaped leaves. 



