Class II. Counter-shaded Leaf-edge Caterpillars. The members of this 

 class are protected by an exquisitely delicate cooperation of obliterative shad- 

 ing with minutely accurate flat-surface mimicry, and this system is variously 

 modified in different branches of the class. But this new principle must be 

 more exactly defined. By cooperation of mimicry with obliterative shading, 

 we mean a resultant mimetic resemblance achieved throughout on a basis of 

 counter shading. Whereas pure mimicry is a matter of the actual form and 

 surface-coloration of animals, irrespective of any artifice of light-and-shade, 

 the mimetic resemblance to a flat leaf-edge in the case of these larvae is achieved 

 by the aid of a delicate system of counter shading. That is, the elaborate single- 

 lea) pattern worn by them looks perfect only when they are so lighted as to bring 

 their whole counter-shaded body to an appearance of perfect flatness; or in 

 other words, their superadded pattern as well as their general surface-color is 

 obliteratively shaded to counteract the effects of the normal high-light and 

 shadow. The markings are lighter, brighter, and sharper in proportion as 

 they are situated on parts of the creature which are normally more averted 

 from the light, and vice versa. (The oak-leaf larva shown in Fig. N is a good 

 example of pure and simple leaf mimicry, as opposed to lea j mimicry dependent 

 on counter shading) This composite scheme might seem to belong rather to 

 obliterative coloration than to mimicry, but we must call it a form of mimicry, 

 for the reason that the resultant resemblance is to part of a definite object 



green pine foliage are almost always of a much more bluish green than those which feed on 

 maple. 



Another interesting example of pigmentation perhaps directly affected by diet is that of the 

 change from green to red undergone by many of the large caterpillars in the autumn, shortly before 

 their transformation into chrysalids, and at precisely the season when many of their food-leaves are 

 turning red. Not only the spinning-caterpillars, such as the Luna and Polyphemus, but also certain 

 of the silkless ones, notably the Basilona imperialis just mentioned, often turn tawny, reddish, or 

 almost bright red, or become strongly tinged with such colors, shortly before they stop feeding, in the 

 late summer or autumn, when they have attained their full size. Thus it cannot be merely a matter 

 of silk-development in their bodies; and it is further noteworthy that the specimens of B. imperialis 

 which develop on pine or spruce trees (spruce is occasionally eaten) rarely or never turn wholly red, 

 while their neighbors of the maple trees are often of a rich copper color, or even brighter, when they 

 descend the trunks to enter the earth. 



188 



