426 Mr. E. B. Poulton. Experimental Proof that the Colours 
where the tough cuticle could not be easily penetrated by their small 
weak mandibles. The larger larve do not experience the same 
difficulty. 
Tt will be well, however, to repeat the experiment with other larvae, 
some of which may be expected to have greater powers of endurance. 
I would suggest Mamestra brassice and Phlogophora meticulosa as 
suitable for the purpose. Freshly cut mid-ribs might be offered 
every day or perhaps twice a day. 
Conclusions from the Experiments—Assuming that the results ob- 
tained in Experiment (2) are not pathological, and I believe that 
this assumption is justified, it follows that etiolin (1), no less than 
chlorophyll (8), can be transformed into a larval colouring matter, 
which may be either green or brown, and is so disposed as to form a 
ground colour. 
The fact that brown pigments may be thus formed is new. In my 
previous paper (‘Roy. Soc. Proc.,’ 1885, pp. 269 et seq.) I gave 
reasons for the conclusion that the green pigments are derived from 
plants, but argued that brown pigments are proper to the larva. 
This still remains true in many cases. Thus the green larve of 
Amphidasis betularia, investigated in 1892, are coloured by derived 
pigments contained in the superficial fat, while the brown larve are 
coloured by true pigment contained in the epidermic cells (‘ Trans, 
Ent. Soc. Lond.,’ 1892, pp. 357—359), so that the green fat which lies 
beneath is concealed. The intensely opaque and dark larvee of many 
other Geometre are probably similarly coloured by true pigments in 
the cuticle or epidermis. But the brown ground colour of many 
Noctua larve will probably be found to be due, like that of 7’. pronuba, 
to modified plant pigments. 
A comparison of the larve fed on pigmentless food (Plate 3, fig. 2, 
Plate 4, figs. 1—3) with those fed upon etiolated leaves (Plate 3, 
fig. 1) and the similar larve fed upon green leaves, proves that both 
green and brown ground colours are modified plant pigments. When 
the larvee fed on etiolin were being compared on October 10, one of 
them became irritated and expelled a drop of fluid from its mouth. 
This fluid was of a faintly blwish-green colour. This observation 
suggests that the change of etiolin into a soluble green pigment takes 
place in the digestive tract. Chlorophyll similarly becomes soluble 
and forms a green solution (turning brown on exposure) in the di- 
gestive tract of larve. It is possible that the brown ground colour 
of the larve is also a result of oxidation: at any rate, it is a change 
in the direction of greater stability ; for I have shown that the colours 
of certain brown larve, evidently coloured like those of 7’. pronuba, 
are far more persistent after preservation than those of the green 
varieties of the same species (‘ Roy. Soc. Proc.,’ 1885, pp. 275, 276). 
Although the brown ground colour, probably situated in this 
