series of high, double-pointed humps, one on each segment back of the front 

 feet, and is further aided by certain markings between and on these humps. 

 Such a caterpillar, therefore, doubtless tends to keep itself adjusted so that 

 the line of its back continues that of the unbroken leaf -edge, from each side of 

 the hole it has gnawed, and in which it is resting. It is also furnished with 

 diagonal darkish lines, one on each segment, which closely resemble the parallel 

 vein-markings on such leaves as elm and birch. Our specimen had no disease- 

 spot representations. The gradation from dark to light (dark on the belly 

 and light on the back, of course, because this is one of the upside-down cater- 

 pillars) is perfect, and the larva's invisibility of course depends primarily 

 on this, as the two figures (K and L) show. Unfortunately, our only specimen 

 was found on the ground, and we cannot be sure what its particular food 

 plant is. The fact that elms were common close about it, as well as its beau- 

 tiful resemblance to the edge of the small elm leaf on which we placed it, 

 make it seem likely that it belongs on this tree. This caterpillar may be said 

 to constitute a separate division of the counter-shaded leaf-edge class, which 

 division we may define as follows: 



Class II, Division A. Involves all the principles assigned to Class II 

 (with the exception, as far as we know, of the leaf -disease-spot picturing), with 

 the additional element of leaf-contour mimicry achieved by humped segments, 

 and pronounced leaf-vein markings. (Fig. K shows the caterpillar in posi- 

 tion, Fig. L inverted.) 



Class II, Division B. The protective coloration of these larvae involves 

 the principles already assigned to Class II, cooperating with an additional 

 distinct element of background-picturing. We have here a new and very 

 wonderful departure from the simple leaf-edge tj^es already described. The 

 caterpillar shown in Plate XIV, Fig. M, a strict leaf-edge inhabitant, is, down 

 to a certain point on its back, exquisitely counter shaded and colored to re- 

 semble the bluish-green upper surface of a beech leaf, its usual food. Its 

 body is even furnished with minute black specks, in apparent imitation of the 

 faintly marbled aspect of the leaf. But this graded green, fading into a pure- 



191 



