of certain Larvce are due to Pigments derived from Food, 429 



fresh, and pale yellow in colour ; that to the left exposed to the air 

 for some hours, and dark brown. 



Fig. 2. A group of three larvee, of the same species, in the 2nd 

 stage, twice the natural size. These larvae had been fed entirely upon 

 the white mid-ribs of cabbage leaves. They had hatched September 

 8, and were painted October 11. While the Iarva9 represented in 

 6g. 1 were rather larger than those fed on green leaves, these are 

 much smaller. The colour is white, and maggot- like, the fainfc 

 greyish appearance being due to superficial true pigment. Except 

 upon the head, there is not a trace of either the green or the brown 

 ground colour invariably found in the larvae of this species nnder 

 normal conditions. Furthermore, these Iarva3 are uniform in appear- 

 ance, although the normal larvae are extremely variable. 



A comparison between figs. 1 and 2 proves that the brown or green 

 ground colour of the species is due to some modification of etioliu 

 (or chlorophyll in the case of normal larvte), unless indeed the results 

 are to be explained as pathological -an interpretation opposed to the 

 facts represented in the figures on Plate 4. 



Plate 4. 



Fig. 1. Out of about fifty larva? which hatched September 8, and 

 were fed on white mid-ribs, a single one began to be conspicuous 

 by its size on November 2, and from this time it grew rapidly, and 

 was evidently quite healthy, although all the others were dead by 

 November 21. On December 2 it was painted (natural size) in 

 two positions, being in the 4th stage. The ground colour remained 

 white or cream-coloured ; the grey effect being caused by superficial 

 true pigment, which is seen to be especially marked upon the brown 

 head, claspers, thoracic legs, prothoracic, and supra- anal plates, and 

 upon the dark subdorsal semilunar marks. 



Fig. 2. The last skin was changed by December 18, and, on the 

 29th, the larva was again painted of the natural size, when advanced 

 in the last stage. The ground colour remained the same, but an 

 increase in the true pigment caused the larva to become a darker 

 shade of grey. A row of supra-,spiracular dark markings also made 

 their appearance. The white subdorsal line and, perhaps, the spira- 

 cular line were evidently due to some cause of colour (probably pig- 

 mentary) distinct from that on which the pale ground colour of the 

 general body surface depended. 



Fig. 3. At the same date the head and anterior segments were 

 painted, X 4 diameters. In those parts where the cuticle is thickened, 

 the head, prothoracic plate, and thoracic legs, a brown ground colour 

 (as well as the black spots and patches) is developed from true pig- 

 ment in the cuticle itself. Hence these parts remain normal when 



