1885.] 



Colouring of Phytophagous Larva?. 



293 



have not yet tried exposing them to the prolonged action of bright 

 sunlight, but they have frequently withstood the effect of its concen- 

 trated rays for several minutes during spectroscopic examination, and 

 have been exposed for weeks to ordinary daylight. 



But while the pigments exist unchanged in the blood of many larvaa 

 for so long a time, in other species they are entirely destroyed during 

 the comparatively short period preceding ecdysis, when some green 

 larvas become brown; and conversely the pigments may appear in the 

 blood equally suddenly. The former change must be due to an active 

 destruction or excretion of the pigments, and is probably also accom- 

 panied by changes in the digestive tract, whereby no more pigment is 

 passed through its walls. And so also, as will be seen, the proportions 

 of xanthophyll and chlorophyll may be changed during the life of a 

 caterpillar. 



The pigments present in the pupal covering of P. Machaon yield to 

 solvent agents far more slowly than in any other place in which I 

 have found them, but this may be due to the resistant nature of the 

 tissue in which they are situated. It cannot be said that they are 

 more stable than the pigments in the blood of the green Ephyra pupa?, 

 for in both alike the pupse are freely exposed to sunlight from autumn 

 to early summer, without the possibility of the renewal of pigment. 



It seems quite certain that the derived pigments of the blood and 

 tissues are only protective, and play no further part in the physiology 

 of these organisms. Thus there are no marked differences between 

 the physiological processes of the brown and green individuals of the 

 same brood in a dimorphic species, or in the processes of a green larva 

 which has become brown, or vice versa. It seems that the pigments 

 are entirely harmless, and are often retained when they would have no 

 effect upon colour. Thus in P. Bucephalus, the blood is bright green, 

 although the larva and pupa are entirely opaque, while the eggs, I 

 believe, are white. It is possible that in this case the conspicuous 

 colours — which warn enemies that the species is distasteful — have 



section has been completely filled and protected by a cover-glass) the blood lias 

 generally remained clear and undecomposed. When, on the other hand, the blood has 

 been sealed up, a little air is unavoidably included, and the fluid generally decom- 

 poses, although tbe pigments are not always destroyed. The blood of the pupa of 

 S. Ligustri was sealed up in a tube (with a little air) on March 20, 18S5. On 

 May 17 the colour and transparency were unchanged, but a whitish cloud had 

 appeared on one side of the tube. On breaking off the end of the tube the contents 

 were found to be putrid and strongly acid, and a large quantity of gas issued under 

 considerable pressure. The whitish cloud was seen to be caused by the presence of 

 large bacteria. The fluid did not clot or blacken on being exposed to the air, and 

 the spectrum of the clear portion showed that the pigments existed unchanged. The 

 spectrum was observed on May 22, five days after the contents of the tube had been 

 exposed to the air and light, and two months after the blood had been taken from 

 the living pupa. — Mav 22, 1835. 



