V 
COLOUR-PHENOMENA IN WORMS 
103 
green of Eulalia viridis , of Sabella , and of many 
others, the pink of Terebella and Euchone rosea , and 
the bright red filaments of Cirratulus , are examples 
of the bright tints which are so widely spread in the 
group. 
Before passing on to consider what is known as 
to the nature of the pigments, we may note the 
different ways in which the external coloration of 
the Annelids is produced. In the smallest and 
simplest forms there is no pigment either in the 
blood or tissues, and the animals are therefore 
transparent and colourless. But when they are 
herbivorous, as is often the case, the contents of the 
food-canal may give them a green colour. The next 
stage may be described as the condition when the 
tissues retain their transparency and lack of pigment, 
but the coloured blood shines through the thin 
body wall, and gives the animals a distinct and often 
bright colour. This is well seen in the bright red 
Tubifex of ditches, the green Sabella in its sand- 
tubes on the seashore, and others. Again, the 
tissues may be devoid of pigment, but may be too 
opaque to allow the blood-pigment to shine through 
except in certain regions. Thus, for example, in 
Gordiodrilus tenuis the general colour is a cream 
white produced by the coelomic corpuscles, but the 
body is marked by longitudinal red stripes produced 
by the shining through of the larger blood-vessels. 
Generally, however, we find that forms in which the 
tissues are too opaque to allow the blood to be 
directly visible not infrequently develop pigment 
in the tissues. Thus the common earthworm con¬ 
tains a certain amount of pigment scattered among 
