The Colotirs of Animals. 85 



also, the streaks are generally wanting in caterpillars 

 which feed on large-leaved plants. The Satyridce, 

 on the contrary, all possess them, and all live on 

 grass. In fact we may say, as a general rule, that 

 these longitudinal streaks only occur on caterpillars 

 which live on or among narrow-leaved plants. As 

 the insect grows, these lines often disappear on 

 certain segments, and are replaced by diagonal 

 lines. These diagonal lines (fig. 12) occur in a 

 great many caterpillars, belonging to the most dis- 

 tinct families of butterflies and moths. They come 

 off just at the same angle as the ribs of leaves, and 

 resemble them very much in general effect. They 

 occur also especially on species which feed on 

 large-leaved plants ; and I believe I may say that 

 though a great many species of caterpillars present 

 these lines, they rarely, if ever, occur in species 

 which live on grass ; while, on the contrary, they 

 are very frequent in those species which live on 

 large-leaved plants. 



3. It might at first be objected to this view that 

 there are many cases, as in the Elephant Hawk- 

 moth, in which caterpillars have both. A little 

 consideration, however, will explain this. In small 

 caterpillars these oblique lines would be useless, 

 because they must have some relation, not only 

 in colour, but in their distance apart, to the ribs 

 of the leaves. Hence, while there are a great 

 many species which have longitudinal lines when 

 young, and diagonal ones when they are older 



