of certain Larva are due to Pigments derived from Food. 427 



species in the epidermic cells, is thus derived, there is an abundant 

 deposit of true pigment in the form of spots arid patches in the 

 superficial cuticle. This was as distinct in the larvae of (2) as in 

 those fed upon etiolin or chlorophyll ; but, the ground colour of the 

 former being white instead of green or brown, it produced a greyish 

 effect (Plate 4, figs. 1 3). The opaque, white stripes in the sub- 

 dorsal and spiracular regions are also probably due to true pigment 

 situated in this case in the epidermic cells, and are equally conspicuous 

 in the larvee fed on pigment! ess food (Plate 4, fig. 2). 



In certain parts of the body the cuticle is of relatively greater thick- 

 ness the head, prothoracic dorsal plate, supra-anal plate, true legs, 

 and parts of the claspers. In these situations, therefore, the com- 

 bination of a deeply- placed ground colour composed of derived pig- 

 ments with a superficially placed true pigment would not necessarily 

 produce the same effect as in the other parts of the body where the 

 cuticle is much thinner ; for the derived pigments would tend to be 

 hidden. In these parts, therefore, both ground colour and markings are 

 cuticular, while both are composed of true pigment of such a tint as to 

 harmonise with the effect produced by the combination of two 

 distinct elements in other parts of the body. Hence these parts 

 remained normal in the larvse of Experiment (2), resembling the 

 brown larvae of the other experiments, and serving to show what the 

 colour of the rest of the body would have been if the plant pigments 

 had been present in the food (Plate 4, fig. 3).* 



Some indication was afforded in the course of these experiments 

 that the power of converting the plant-pigments into metachlorophyll 

 may be lost in larvae which have been fed from the egg for a con- 

 siderable time upon pigmentless food. Thus the larvae of Experiment 

 (2) remained pale when fed upon leaves which caused those of Ex- 

 periment (1) to become brown or green. At the same time it must 

 be remembered that these particular larvse were certainly unhealthy, 

 and died soon after the change of food. I hope to repeat this experi- 

 ment upon healthy larvae. I have already shown that many larvae 

 which are normally found upon a variety of food plants will starve 

 rather than eat certain of them when they have been fed upon the 

 others from the egg ('Ent. Soc. Lond. Trans.,' 1887, pp. 312314). 

 It is possible that a somewhat analogous " gastric education " may 

 take place as regards the digestive action upon plant pigments. But 

 conBrmatory experiments, specially directed to test the conclusion, 

 are much wanted. 



* [This argument appears to be valid in the case of the older larvae of this species 

 and probably many others. There are, however, many instances in which the 

 derived pigments are distinctly visible through an extremely thick cuticle (e.g., in 

 the head of larvae of the genus Smerinthus). The distribution of the derived pig- 

 ments has not been investigated in this case. October 15, 1893.] 



