1885.] Colouring of Phytophagous Larva?. 291 



(or even whether there are more than one. The immense complexity 

 of the subject and the many shades of opinion are seen in a paper by 

 Dr. A. Tschirch, " On the Preparation of Pure Chlorophyll," " Journ. 

 of Chem. Soc," February, 1884, p. 57). 



Nevertheless, the difference between the spectrum of the yellow 

 covering of P. Machaon and of its yellow blood, is just that figured 

 by Mr. Sorby in his paper already quoted — a shifting of both the 

 bands towards the violet end in the former case. At the same time it 

 is probable that there is a difference in the animal substance with 

 which the pigment is associated in these two cases, and this may 

 account for some difference. The chlorophyll cannot have exercised a 

 modifying effect on the results given above as due to xanthophyll 

 (Chart, Spectrum 6), for when the spectrum of the latter was seen 

 in the unaltered blood, the thickness employed was so slight that the 

 band of chlorophyll in the red could not be Vv seen, and further yel- 

 lowish blood was made use of. In the blood of P. Machaon the 

 bands of chlorophyll could not be seen even in a considerable 

 thickness. When green blood {e.g., P. Bucephalus) was examined 

 for xanthophyll, the latter was obtained in ethereal or alcoholic 

 solution (the chlorophyll always disappearing with the latter solvent, 

 becoming fixed in the solid state with the latter). On the other 

 hand it is certain that the bands of xanthophyll are present in the 

 spectrum of green blood (such as P. Bucephalus, Spectrum 3), the 

 first band being contained in that from 52 — 48, and the second 

 being rendered invisible because of the greater darkening of the violet 

 between 48 and 42. The extreme absorption of the violet end shown 

 in Spectrum 2 ($. Ligustri) is due to chlorophyll, xanthophyll, and, 

 possibly, lichnoxanthine ; and in this general absorption the chloro- 

 phyll takes a small part as compared with the next spectrum (Chart 3), 

 as is at once seen on comparing their absorption at the red end. 



11. Conditions under which the Derived Figments exist in the 



Larvce, 8fc. 



There is one essential difference between the chlorophyll (especially) 

 in solution in caterpillar blood or tissues, and all other solutions of the 

 same substance, in the great stability of the former under the pro- 

 longed action of light. The necessity for this is obvious, inasmuch 

 as the colour of the larvse often depends upon their complete translu- 

 cence (P. Meticulosa, &c), and very many of them rest in such a posi- 

 tion as to be freely exposed to direct sunlight. Furthermore there are 

 long pauses in larval life, during which no food is taken to renew 

 the derived pigments. Such occur at the various ecdyses, and the 

 colours do not fade at these times, nor when the larvse are from any 

 cause deprived of food. Hence it is seen that the pigments, having 



