114 COLOUR IN NATURE chap. 



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 

 zocecium 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 



