PROTECTIVE COLORATION AND DEFENSIVE STRUCTURES OF LARV.E. 89 



dark brown, 3 brown, 2 greenish-brown, 2 green (one larva disappeared). 

 Larvae of Catocala nupta also responded very readily to differences of 

 environment, the change consisting of the normal colour becoming 

 lighter or darker, and the markings varying in intensity, although the 

 difference between the most extreme forms from light and dark sur- 

 roundings, respectively, was very great. C.fraxini also responded readily, 

 5 lame, in dark-coloured surroundings, becoming brownish-grey in 

 colour, 5 others, in green surroundings, becoming bluish-green. Poulton 

 extended the results obtained by Miss Gould in Catocala, by showing 

 that C. sponsa, C. electa and C. elocata were also susceptible to colour 

 influences in their environment. One cannot help remarking here 

 that the number of larvae experimented upon, although affirming the 

 principle, is quite insufficient to base any sweeping generalisations 

 upon. Poulton has further shown that larvae of AmpMdasys betularia, 

 Sdenia lunaria, Puiinia luteolata, Melanippe montanata, Crocallis eliny- 

 uaria and Hemerophila abruptaria, are highly sensitive, and that larvae 

 of Ennomos quercinaria (anyularia), in addition, are greatly influenced 

 by actual darkness. This latter result, Poulton states, is exceptional, 

 for larvae brought up in total darkness are usually lighter than those 

 reared among an abundance of dark twigs in strong light. 



The structural cause of the variation in the colours of Amphidasys 

 betularia was investigated by Poulton. He found that the colour of 

 the larva was in the skin, or just below it. In all the larvae experi- 

 mented upon, he found that the colour of the fat just below the skin 

 was green, in some brown larvae it was a bright green, as in the green 

 ones. This green fat was found to contain green colouring matter 

 (probably some derivation of chlorophyll) in the oil globules within the 

 cells. When the epidermis is comparatively clear, the green colouring 

 matter shows through, but when the epidermis contains a dark pig- 

 ment, the skin is interposed like a screen outside the green fat, and the 

 larva takes on the appearance or tint of the darkened epidermis. In 

 green larvae the epidermal layer, covering the green fat, contains a 

 substance of a light yellow transparent colour, that appears greenish- 

 yellow under the microscope, the cuticle itself being colourless, except 

 for certain small brown spots. The darker larvae obtain their colour 

 from a dark pigment contained in the epidermal cells, which thus con- 

 ceal the subjacent green fat, so that, if we accept Poulton's explanation, 

 it would seem that the reflection of the light from the surrounding 

 objects has to produce such nervous action as results in an actual 

 physiological change in the deposition of pigmentary matter in the 

 epidermis. Poulton suggests that some quality of the light brings 

 about the change, but of the actual mechanism that produces this 

 result, we know absolutely nothing. 



Packard says that it is possible that the close resemblance of the 

 warts, projections and spines of certain arboreal caterpillars, which 

 so closely mimic the spines, leaf scars, and projections of the branches 

 or twigs of plants, has been brought about in a way analogous with the 

 production of spots and lines on the body of caterpillars. Darwinians, 

 he says, attribute this to the action of " protective mimicry," but 

 this expression rather states the result of a series of causes. The 

 effect of dark and light shades, and the light and shade, in producing 

 the stripes and bars of caterpillars, is comparatively direct and mani- 

 fest ; but how can thorns and other projections, on trees and shrubs, 



