V 
COLOUR-PHENOMENA IN WORMS 
107 
superficial coloration. The deposition of pigment 
either in the cuticle or in the hypodermis is rare, 
but in Capitella and Heteromastus granules and 
droplets of yellow-brown pigment lie between the 
cuticle and the hypodermis in patches. As the 
nephridia contain similar granules, Eisig is of opinion 
that these pigment patches are due to substances 
excreted by the nephridia which do not reach the 
surface but, lying in the skin, are got rid of at the 
(hypothetical) moult. In Capitella, in the head and 
tail regions, the skin is of a red-yellow colour, which 
is due to clusters of blood-discs containing excretory 
particles again lying between the cuticle and hypo¬ 
dermis. According to Eisig these blood-discs, after 
they have taken up excretory particles, lose their 
power of circulating and stagnate at the areas in the 
skin mentioned above. Further, Eisig considers that 
the pigment is directly derived from the haemoglobin 
of the blood, that it occurs in the nephridia in 
association with guanin as one of the nitrogenous 
waste products of the organism, and that it may 
find its way to the skin and bristles and there be an 
important agent in coloration. He therefore con¬ 
cludes that pigment is always, or at least frequently, 
in origin a waste product eliminated by the skin. 
This is of course a position which has been advo¬ 
cated or supported by many writers, and that such 
a utilisation of waste product does occur has now 
been abundantly proved, eg. in Lepidoptera ; that 
it occurs in Annelids is eminently probable, and is 
rendered more so by Grafs observations on leeches, 
to which we shall afterwards refer. At the same 
time it is perhaps permissible to remark that it does 
