COLOUR IN NATURE 
CHAP. 
114 
that the leucocytes of the funicular tissue, the so- 
called hepatic cells of the alimentary canal, and to a 
less degree the cells of the funicular tissue itself, all 
took up the pigment. When the polypides began 
to degenerate, which perhaps occurred sooner on 
account of the treatment, the leucocytes became 
more or less aggregated round the brown body, 
while the pigment of the alimentary canal took a 
direct part in the formation of the brown body. The 
new-formed polypide is entirely devoid of artificial 
pigment, which is either stored up within the 
zooecium or in part eliminated with the brown body. 
The introduced pigments are thus eliminated from 
the living tissues, the active agents being the three 
sets of cells already named. The funicular tissue 
took up pigment most readily in the case of 
Bugula neritina , the species in which it is normally 
pigmented. 
Now as the alimentary canal of very young 
individuals shows no pigment in its cells, and as 
this pigment subsequently appears in gradually 
increasing amount in cells which certainly excrete 
introduced pigment, Harmer is of opinion that the 
view that the formation of the brown body is an 
excretory process is well founded, and that the 
brown pigmentary substance is a waste product, or 
at least a useless substance. The view is further 
confirmed by the fact that indigo-carmine, when 
introduced into the body cavity of other animals, 
is excreted by cells which are certainly excretory in 
nature. 
It almost seems, however, as if we might go 
farther than this. It appears that the leucocytes 
