of certain Larvae 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 and patches in the 
superficial cuticle. This was as distinct in the larve 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 pigmentless 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 larve of Experiment (2), resembling the 
brown larvee 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 larve which have been fed from the egg for a con- 
siderable time upon pigmentless food. Thus the larve 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 larvee were certainly unhealthy, 
and died soon after the change of food. I hope to repeat this experi- 
ment upon healthy larve. I have already shown that many larvee 
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. 312—314). 
It is possible that a somewhat analogous “ gastric education” may 
take place as regards the digestive action upon plant pigments. But 
confirmatory experiments, specially directed to test the conclusion, 
are much wanted. 
* [This argument appears to be valid in the case of the older larvex 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 larve of the genus Smerinthus). The distribution of the derived pig- 
ments has not been investigated in this case.—October 15, 1893. ] 
