100 
COLOUR IN NATURE 
CHAP. 
green in colour, and was for long supposed to 
contain chlorophyll. The pigment is said to occui 
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 spectium, 
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 
chaetopterin 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, 
