of certain Larve 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 larve, of the same species, in the 2nd 
stage, twice the natural size. These larve had been fed entirely upon 
the white mid-ribs of cabbage leaves. They had hatched September 
8, and were painted October 11. While the larve represented in 
fig. 1 were rather larger than those fed on green leaves, these are 
much smaller. The colour is white, and maggot-like, the faint 
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 larve of this species under 
normal conditions. Furthermore, these larvee are uniform in appear- 
ance, although the normal larve 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 etiolin 
(or chlorophyll in the case of normal larve), 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 larvee 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 
