The green grass-eating caterpillar of many of our _Satyridæ_ has two or more darker or lighter lines running down the sides of its body, which make it much less conspicuous among the grasses on which it feeds than if it were a uniform green mass (Fig. 2). Not infrequently the colour and form present a remarkably close resemblance to the inflorescences or fruit-ears of the grasses. Caterpillars marked thus are never found on the leaves of trees, where they would immediately catch the eye. It is true that longitudinal striping often occurs on caterpillars which live on other plants besides grass, but as these other plants grow among the grasses the protective efficacy is just the same. This is the case with the Pieridæ (Garden Whites). All the caterpillars of our Sphingidæ, on the other hand, which live on bushes and trees, have on the sides of the segments light oblique stripes, seven in number, which are disposed to the longitudinal axis of the body at the same angle as the lateral veins of a leaf of their food-plant have to the mid-rib. It cannot of course be said that the caterpillar thereby gains the appearance of a leaf, indeed, if one sees it apart from its food-plant it does not look in the least like a leaf, but among the leaves of a bush or tree this marking secures it in a high degree from discovery. Thus the caterpillar of the eyed hawk-moth (_Smerinthus ocellatus_), when it is sitting among the crowded foliage of a willow, is often very difficult to find, because its large green body does not appear as a single green spot, but is divided by the oblique lateral stripes into sections like the half of a willow leaf, so that even a searching glance is led astray, there being nothing to focus attention on the animal as distinguished from its surroundings (Fig. 3). As a boy I often had the interesting experience of overlooking a caterpillar which was sitting just before me, until after a time I chanced to hit upon the exact spot in the field of vision. [Illustration: FIG. 2. Longitudinally striped caterpillar of a Satyrid. After Rösel.] [Illustration: FIG. 3. Full-grown caterpillar of the Eyed Hawk-moth, _Smerinthus ocellatus_. _sb_, the subdorsal stripe.]