V 
COLOUR-PHENOMENA IN WORMS 
109 
“ beautiful,” as applied to it, is advised to examine the 
plates illustrating Whitman’s Memoir on the Leeches of 
Japan , where the native draughtsman has delineated 
the colouring with a fidelity which Western artists 
can only envy and admire. 
The pigments of leeches are largely of the dark, 
insoluble, and little-known type, but it is probable 
that lipochromes are also often present. What part, 
if any, the haemoglobin of the blood takes in colora¬ 
tion is unknown. 
On the origin of the pigment and markings of 
leeches there is an exceedingly interesting paper by 
Dr. Arnold Graf. According to this investigator 
there are in leeches certain migratory cells, compar¬ 
able to the yellow cells of the earthworm, which 
arise from the endothelium of the body cavity, 
receive waste products from the blood-vessels, and 
carry these to the nephridia and so to the exterior. 
The waste products received by these “ excreto- 
phores ” are of the nature of fine dark granules, 
which are capable of acting as a pigment. Graf 
finds that all the excretophores do not reach the 
neighbourhood of the nephridia, but that certain of 
them penetrate the musculature of the body, and 
come to lie immediately beneath the epidermis, 
where the contained dark-coloured granules give rise 
to surface coloration. He further states that the 
number of the excretophores and the intensity of the 
pigmentation increase with age, and when, as in 
albino varieties, pigment is scarce, the excretophores 
are also greatly reduced in number. The amount of 
pigment appears to depend upon the intensity of 
metabolism, being greatest in the most voracious 
