i8 9 6. THE PIGMENTS OF ANIMALS. 99 



number of eggs of Tvyphcena proimba, and divided them into three sets. 

 From the time of hatching, the three sets of larvae were kept under 

 similar conditions in the dark, and were fed respectively with the 

 yellow etiolated leaves from the heart of a cabbage, the white midrib 

 from which the yellow blade had been removed, and the ordinary 

 green outer leaves of a cabbage. Of the three sets, the first and 

 third developed well and showed almost identical colouring, the 

 colour being in the early stages usually pale green, or occasionally 

 dark green, but all turned brown, mostly dark brown, when maturity 

 was reached. In this last respect they were contrasted with control 

 specimens developed in the light, as these usually retained the green 

 colour until maturity. This was apparently the only effect produced 

 by the absence of light, which was necessary to avoid the risk of the 

 conversion of etiolin into chlorophyll. In the second set, those fed 

 with white midribs, the mortality was very great, only one larva out 

 of a great number attaining complete maturity. The growth of these 

 larvae throughout was extremely slow, and they were invariably 

 devoid of green colour, although the cuticular pigment was developed 

 as completely as in normal larvae. 



Mr. % Poulton's conclusion is that this experiment, taken in 

 connection with previous observations on the nature of the pigment, 

 tends to prove that the green or brown colouring matter in this species 

 is derived from the pigments of the food, and may owe its origin 

 either to etiolin or to chlorophyll. The experiment proves also that 

 the cuticular pigment does not depend for its development upon the 

 nature of the food. Mr. Poulton notes that the unhealthy appearance 

 of the second set of larvae may of course be held to indicate that it 

 was owing to constitutional weakness that the larvae were incapable 

 of forming the green or brown pigment, and not to the lack of 

 pigment in the food; but this is rendered improbable by the following 

 considerations. The unhealthiness of the larvae was most probably 

 due to the fact that the white stalks upon which they were fed were 

 so hard that it was difficult for them to obtain sufficient food, 

 especially in the early stages when the mandibles were weak. (We 

 might suggest that, in a repetition of the experiment, chlorotic leaves 

 would be a fairer test.) Further, the single larva which did attain 

 maturity was large and apparently in no way unhealthy. Again, the 

 normal development of the true or cuticular pigment certainly 

 suggests that the ordinary green pigment is in some way connected 

 with the food. It is interesting to note that either etiolin or 

 chlorophyll can produce the adventitious pigment of the larvae. 

 Both seem to undergo similar changes in the digestive tract, and in 

 the altered condition find their way to the tissues. The whole of the 

 pigment taken in with the food is apparently not retained within the 

 body, for it was noticed that the faeces in the case of the first and 

 third sets of larvae were always yellow when fresh, but after exposure 

 to the air oxidised and turned brown. This may be compared to the 



