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 epidermic 

 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 



