ON CERTAIN GREEN PIGMENTS IN INVERTEBRATES. 399 



acidified solution is witliout fluorescence. In the case of 

 chsetopterin tlie fluorescence ceases to be marked when the 

 solution is very strongly acid, but when a ray of bright light 

 is thrown upon the vessel containing the solution placed against 

 a dark background, it rarely fails to show a trace of the charac- 

 teristic blood-red colour. The more detailed characters of the 

 blue and green solutions it may be well to study separately. 



The Blue Acid Solution. — When acid is added to an 

 alcoholic solution of chsetopterin the solution becomes more 

 or less turbid in appearance. If a considerable amount of acid 

 be added, and then water, and the whole shaken in a separation 

 funnel, the superficial layer of ether becomes pale green, the 

 lower layer a pure clear blue with marked fluorescence. 



(a) The ether gives more or less distinctly the original 

 four bands of chsetopterin without the band at the right of D. 

 When weak the band in the red has its centre about A 661 — 

 the position of that of the original solution ; but if the ether 

 contains much pigment the centre of the band tends to shift to 

 the right, and to approach more closely that of the band of the 

 acid solution. In other words, the spectrum may be that of 

 fig. 1, but there is a tendency for the first band of it to be 

 replaced by the first band of fig. 2, or by a band intermediate 

 between the two. When the ether is evaporated and the pig- 

 ment dissolved in methylated spirit a green solution is formed, 

 with little fluorescence. On adding acid the solution does not 

 turn blue ; it shows at first little alteration, and later becomes 

 brownish. The pigment is thus altered, — is not identical 

 with neutral chajtopterin. At the same time it is to be noticed 

 that the amount of alteration varies greatly. In some cases 

 the ether seems to give the full four-banded spectrum of fig. 1 

 without alteration ; in other cases it may give only a band in 

 the red, corresponding to the first of fig. 2. The green tint 

 and the absence of the power of giving a blue colour with acid 

 are the most constant characters. 



(b) The blue acid solution left after shaking with ether 

 gives the same spectrum as it did before the process. When 

 strong it is a beautiful pure blue colour, but in some cases 



