100 COLOUR IN NATURE chap. 



green in colour, and was for long supposed to 

 contain chlorophyll. The pigment is said to occur 

 in the skin and sub-epidermic cells of the female, 

 and in the wandering cells which partially fill the 

 reduced body cavity in the degenerate male. It is 

 readily soluble in alcohol, the solution being green 

 to brown according to the degree of concentration, 

 and displaying a blood - red fluorescence. The 

 solution gives a beautiful and complex spectrum, 

 which changes when acid is added. The addition 

 of acid also changes the colour from violet to blue 

 according to the amount added. The pigment was 

 given the name of bonellin by Sorby, and has been 

 studied by numerous investigators. Both Sorby 

 and Krukenberg showed conclusively that it is not 

 chlorophyll, but the superstition dies hard, and may 

 be still found in many text-books. Professor E. 

 Ray Lankester (1897) has recently re-examined the 

 pigment, and shown that it occurs in the organism 

 in the alkaline condition — a point of some interest. 

 There can be little doubt that bonellin is a member 

 of the group of pigments spoken of in the last 

 chapter, which may conveniently be called the 

 chsetopterin group. These pigments contain nitrogen 

 but no copper, and their function is quite unknown. 

 The curious point in connection with bonellin itself 

 is that it is only known in Bonellia viridis, although 

 a green colour is common among the Echiuroids. A 

 new British species of Thalassema, described by 

 Professor Herdman, is of an extremely vivid green 

 colour, the tint being somewhat similar to that of 

 Bonellia. Nevertheless the pigment was found to 

 be soluble in water, to give a one-banded spectrum, 



