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 
