To this category belong all the species of _Sesiidæ_ (the genera _Sesia_, _Trochilia_, _Sciapteron_, _Bembecia_, &c.), the larvæ of which, without exception, are of a whitish or yellowish colour, and live partly in the wood of trees and shrubs and partly in the shoots of herbaceous plants. Subterranean larvæ also, living at the roots of plants, such as _Hepialus Humuli_ at the roots of hop, and _H. Lupulinus_ at those of _Triticum Repens_, possess neither colour nor marking. These, like the foregoing, are yellowish-white, evidently because they are deprived of the influence of light.[142] The larvæ of certain small moths, such as _Tortrix Arbutana_ and _Pomonana_, which live in fruit, and many case-bearing _Tineina_, are likewise without marking and devoid of bright colour, being generally whitish. Many of the small caterpillars which feed exteriorly are also--so far as my experience extends--without definite markings, these being among the most minute, such as the greenish leaf-mining species of _Nepticula_. It is among the larger species that we first meet with longitudinal and oblique stripes. Eye-spots do not occur in any of these larvæ, a circumstance of the greatest importance for the biological significance of this character, as will be shown subsequently. The small size of the caterpillars cannot be the sole cause of the absence of such eye-spots, since in young _Smerinthus_ caterpillars one centimeter long, the oblique stripes are beautifully developed, and the larvæ of many of the smaller moths considerably exceed this size. The surface of these caterpillars therefore, _i.e._, the field on which markings are displayed, is not absolutely too small for the development of such a character. Besides the larvæ of the Micro-lepidoptera and of those species living in the dark, there is also a complete absence of marking in the young stages of many caterpillars. Thus, all the _Sphingidæ_ of which I have been able to observe the development, show no markings immediately after emergence from the egg; in many they appear very soon, even before the first moult, and, in other species, after this period. 2. _The second category of markings, longitudinal stripes_, is very widely distributed among the most diverse families. This character is found among the larvæ of butterflies, _Sphingidæ_, _Noctuæ_, Micro-lepidoptera, &c., but in all these groups it is absent in many species. This last fact is opposed to the view that this character is purely morphological, and leads to the supposition that it may have a biological value, being of service for the preservation of the individual, and therefore of the species.