ON CERTAIN GREEN PIGMENTS IN INVERTEBRATES. 401 



chaetopterin there is an acid derivative corresponding to 

 Krukenberg's bonellidin. As already seen, bonellidin is the 

 pigment supposed to be present in a solution of bonellin turned 

 violet by acid ; it is characterised by its colour and its spec- 

 trum. The spectrum is distinguished from that of neutral 

 bonellin by the different position of especially the band in the 

 red, the appearance of a new band analogous to that at the right 

 of D in the case of chsetopterin, as well as by the loss of the band 

 in the violet. Blue acid solutions of chsetopterin are character- 

 ised by the (slight) change of position of the band in the red, the 

 apparent loss of the band in the violet, and a slight change in 

 the position of the other bands, as well as by a colour-change 

 as contrasted with neutral solutions. But the band to the 

 right of D is present as a shadow in neutral solutions, and is 

 only marked when the solution examined actually contains 

 acid. Thus, if a solution of the pigment in anhydrous ether 

 be vigorously shaken with acid, this band, previously a mere 

 shadow, becomes suddenly distinct. If the ether be then 

 carefully washed with distilled water to remove any trace of 

 acid, the band disappears. This seems to me to prove that the 

 appearance of this band is not due to the formation of a com- 

 pound, for it is difficult to believe that a true compound could 

 be so extraordinarily unstable. Krukenberg noticed a similar 

 fact, that an evaporation of solutions of bonellin containing a 

 volatile acid caused the disappearance of the corresjionding 

 band; he calls this the regeneration of bonellin from bonellidin, 

 but I cannot agree to this conclusion. 



Again, the loss of the band in the violet is a point of no 

 importance, for it may be quite easily explained as the result 

 of tiie slight turbidity of the solution, and the change in posi- 

 tion of the other bands is too slight to be of any moment. I 

 thus dissent from the view that the spectrum and the colour 

 of the blue acid solution are together diagnostic of the ex- 

 istence of a new pigment defined by these characters, and 

 believe that the point which requires explanation is that the 

 action of dilute acid is to produce a permanent alteration in 

 the position of the band in the red solutions in chsetopterin, and 



