358 Mr. Vonlton.' a farther experiments upon 



digestive tract. But I do not think any effect is pro- 

 duced in the normal state when the larva is less 

 stretched, and the superficial coloured layers are there- 

 fore thicker, and when the light has to penetrate the 

 larval skin before reaching the blood and internal organs; 

 so that the latter cannot be highly illuminated as they 

 were in the dissection. 



In all larvae the layer of fat between the superficial 

 muscles and the epidermis (hypodermis) was more or 

 less green. In green varieties it is bright green, and 

 causes the colour of the larva, as is at once seen if a 

 small area be removed. In some brown larvae it is quite 

 as green as in the green ones, but is concealed by dark 

 pigment in the epidermis, which acts as a screen. In 

 others the colour is developed but little, and in one dark 

 larva examined this fat was pale yellowish green, except 

 in the first abdominal segment, where it was as strongly 

 coloured as in a green larva. If a little of the green fat 

 be removed and examined under the microscope, it is 

 seen to be opaque and bright green. It can be made 

 thinner by pressure, and thus rendered transparent, 

 when it appears as a pale yellowish green. High powers 

 show that the green colouring matter (probably some 

 derivative of chlorophyll) is contained in the oil-globules 

 within the cells. Alcohol instantly turns the fat deep 

 yellow, and causes the oil-globules to be compressed out 

 of the cells, and to cohere in large yellow drops, gradually 

 decolorised by the alcohol, which becomes itself tinged 

 with the same colour. 



The dark pigment is contained, as I have said, in the 

 epidermis cells, which lie over this layer of fat, thus con- 

 cealing the latter. In green larvae the epidermal layer 

 covering the green fat contains a light yellow transparent 

 colour, appearing greenish yellow under the microscope. 

 It dissolves out in alcohol, and is probably some chloro- 

 phyll derivative. The cuticle is colourless, except for 

 certain small brown spots. 



Intermediate larvae are well suited for displaying both 

 these causes of colour. These are commonly green, 

 with a distinct wide brown dorsal stripe, which, ante- 

 riorly in each segment, passes downwards, and forms a 

 ghdle round the larva ; while posteriorly the green 

 colour forms a broader girdle, interrupted in the dorsal 

 region by the brown stripe. If such a larva be pinned 



