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, e.g. in Lepidoptera ; that 

 it occurs in Annelids is eminently probable, and is 

 rendered more so by Graf's observations on leeches, 

 to which we shall afterwards refer. At the same 

 time it is perhaps permissible to remark that it does 



