V COLOUR-PHENOMENA IN WORMS 115 



in Polyzoa have not any power of taking up pigment 

 from the so-called hepatic cells of the gut and carry- 

 ing it outwards, as they have, for example, in the 

 Capitellidae, where carmine introduced into the gut 

 is carried outwards to the skin by the action of 

 leucocytes. Is it too daring a suggestion that the 

 mysterious process of regeneration in the Polyzoa is 

 due to the want of such a mechanism, and the con- 

 sequent choking of the important "hepatic" cells 

 with noxious substances ? The drastic measure of 

 total reconstruction may thus be compelled by the 

 poisoning of essential cells. 



This discussion may seem somewhat irrelevant 

 to our main subject, but it is in reality of much 

 importance in connection with theories as to the 

 origin of pigment. In Polyzoa the cells of the gut 

 are deeply pigmented with an apparently useless 

 substance, and there is no mechanism by which 

 leucocytes can carry away this pigment. In many 

 animals the cells of the gut, or the hepatic cells,, 

 contain pigment, and the leucocytes have the power 

 of removing pigment from these cells to the skin or 

 to the exterior ; are we therefore justified in regard- 

 ing such skin pigments as waste products ? This is 

 a question which we shall have to consider in some 

 detail later. The suggestion is one which has been 

 repeatedly made under various forms, and it is bound 

 up with some interesting questions in relation to 

 colour problems. 



It should be further noticed that the purple 

 pigment of Bugula neritina disappears for a certain 

 period during the development of the young poly- 

 pides, and then reappears later. Harmer differs from 



