It can easily be demonstrated that longitudinally striped caterpillars mostly live on plants, of which the general appearance gives the impression of a striped arrangement. We have only to consider in connection with their mode of life, any large group of adaptively coloured species marked in this manner. Thus, among the butterflies, nearly all the _Satyrinæ_ possess larvæ conspicuously striped--a fact which is readily explicable, because all these caterpillars live on grasses. This is the case with the genera _Melanargia_, _Erebia_, _Satyrus_, _Pararge_, _Epinephele_, and _Cænonympha_, no species of which, so far as the larvæ are known, is without longitudinal stripes, and all of which feed on grasses. It is interesting that here also, as in certain _Sphingidæ_, some species are brown, _i.e._, adapted to the soil, whilst the majority are green, and are therefore adapted to living grass. Just as in the case of the _Sphingidæ_ also, the brown species conceal themselves by day on the earth, whilst some of the green species have likewise acquired this habit. I have already shown how this habit originates from the increasing size of the growing larva, which would otherwise become too conspicuous, in spite of adaptive colour and marking. A beautiful confirmation of this view is found in the circumstance that only the largest species of _Satyrus_, such as _S. Proserpinus_, _Hermione_, _Phædrus_, &c., possess brown caterpillars. I should not be surprised if a more exact investigation of these species, which have hitherto been but seldom observed, revealed in some cases a dimorphism similar to that of the _Sphingidæ_; and I believe that I may venture to predict that the young stages of all these brown larvæ--at present quite unknown--are, as in the last-named group, green.