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



Comparing these two spectra with, those of green blood (not yellow) 

 (Chart, Spectra 1, 2, and 3), the resemblance is seen to be very- 

 great, the chief differences being in the second and third bands of the 

 red end, which are continuous (Chart, Spectra 2 and 3), while the 

 third is developed before the second (Chart, Spectrum 1). Considering 

 the chemical change which must have taken place in the chlorophyll 

 during digestion, rendering possible the passage of the walls of the 

 digestive tract, and considering its chemical union with a proteid 

 constituent of the blood, the resemblances of the spectra are very 

 striking ; in fact, the two spectra are far nearer to each other than the 

 ordinary spectrum of chlorophyll in alcoholic solution is to the unal- 

 tered chlorophyll of leaves. I believe, however, that the perfectly 

 fresh alcoholic solution gives a spectrum resembling that of the leaf, 

 but the spectrum changes in a few seconds, so rapidly is the solution 

 acted on by light. I have never seen a band in the green in cater- 

 pillar's blood, and yet the blood is acid (Mr. Sorby states that any dis- 

 tinct band in the green is due to acidity).* I have not been able to 

 satisfy myself of the fluorescence of green caterpillar blood, certainly 

 there is not the marked red fluorescence of the alcoholic solution of 

 chlorophyll. But this red fluorescence is not present in leaves, nor in 

 the perfectly fresh solution, according to J. B-einke (" Bied. Centr.," 

 1884, 692—696, abstracted in " Jour, of Chem. Soc." February, 1885, 

 ii, 182). The points of difference between the derived xanthophyll 

 spectrum of caterpillars (shown in Chart 6) and that figured by 

 Mr. Sorby (" Proc. Roy. Soc," vol. 21, No. 146, p. 442) is the occur- 

 rence of a third band in the former, the variable thickness of the 

 second band and difference in darkness between it and the first, and 

 the complete absorption of the violet end. It is possible that the latter 

 may be due to one or more of the lichnoxanthines, while the third 

 band is not always present, and is probably that to which Mr. Sorby 

 alludes when he states (concerning the xanthophylls) that " some- 

 times three absorption-bands may be seen; but in that case it is 

 generally easy to prove, either by chemical or photochemical methods, 

 that the third band is due to a second substance." This third band 

 was only seen in the best daylight with the greatest care, and it was 

 never present in the alcoholic solution obtained from larvse and pupae, 

 which gave the other two bands. It is rather a barren question to 

 discuss whether more than one derived xanthophyll is present, until 

 the botanists have agreed upon the classification of these substances 



* The spectrum of Ephyra blood is the same as that of the leaf, except in the 

 absence of the third band ; the slight difference in the chief band in the red being 

 explained by difference in the amount of pigment examined. I think it is very 

 probable that a sufficient thickness of this blood will give a spectrum identical 

 with that of the lepf, but nevertheless the derived pigment must have been changed 

 in such a way as to render it stable in solution. — May 4th, 1885. 



