292 Mr. E. B. Poulton. Essential Nature of the [Apr. 23, 



reached the blood or tissues, are in a state of great stability, and do 

 not require renewal. The same thing is even more forcibly shown in 

 the persistence of the pigments in the pupae, and on into the ova and 

 young larvae of the next generation. But comparing these young 

 larvae before and after their first meal, and remembering that their 

 latter appearance more resembles the one that they will permanently 

 keep (if they remain green), it is obvious that something has been 

 lost to the derived pigments in the interval between pupation and the 

 hatching of the ova (often six months, or longer) ; and the constituent 

 that has been partially lost is the more unstable of the two under all 

 circumstances — the chlorophyll. It is not likely that the chlorophyll 

 is partially eliminated by the action of light, for the pupal period 

 is in nearly all cases passed in the dark. But it seems probable 

 that pigment is lost in the various phases of redistribution gone 

 through, as solution in fluid and deposition in tissue alternate. It is 

 perfectly certain that the essential difference in colour between the 

 newly-hatched larva (of a green species) and one that has fed, is the 

 predominant yellow tinge and translucence of the former, and the 

 green tinge and comparative opacity of the latter (not entirely due to 

 the digestive tract being full). 



The same unusual stability is also true of the xanthophyll, and 

 must be due to the same cause, association with a proteid of the 

 blood or tissue. The separation of the pigments from any con- 

 stituent of the blood is at once effected by the addition of alcohol. 

 If absolute alcohol be employed, the proteids are precipitated with 

 the colouring matter, but the xanthophyll at once enters into 

 solution in the alcohol, colouring it yellow, while the chlorophyll 

 disappears, and the proteids are decolourised. This must be due 

 to the extreme instability of the chlorophyll, at any rate in the 

 presence of alcohol when separated from the proteid, so that it 

 breaks up into colourless compounds when separated from it. The 

 xanthophyll dissolved in the alcohol slowly decomposes in daylight, 

 but lasts for many weeks, the colour gradually fading. Ether, on the 

 other hand, precipitates the combined pigments and proteid in the 

 form of a green jelly (the upper part is generally darkened), and for 

 some hours dissolves no coloured constituent. Eventually, however, 

 it becomes bright yellow with xanthophyll ; while if the green 

 coagulum be broken up in the ether more xanthophyll is dissolved, 

 and a small quantity of green fluid containing chlorophyll remains at 

 the bottom. This, however, is not dissolved in ether. The frag- 

 ments of the coagulum undergo no apparent change. 



If on the other hand the blood be protected from the air, the pig- 

 ments seem to exist indefinitely, and the fluid does not decompose.* I 



* In those instances in which the air has been entirely excluded (when a tube 



