V COLOUR-PHENOMENA IN WORMS 99 



difference in colour, but in some cases, as in Amphi- 

 porus pulcher, the eggs are bright red, and by shining 

 through the thin body wall, produce a striking effect 

 on the coloration of the female. In simple animals 

 this primitive form of colour-difference in the sexes 

 is not uncommon. 



Burger's recent monograph with its beautiful plates 

 confirms M'Intosh's descriptions without adding very 

 much new information as to colour. Burger describes 

 the epithelium as consisting of three kinds of cells — 

 slender thread-like cells, interstitial cells, and gland- 

 cells. The abundant pigment may occur in any of 

 the three. In Lineus and the related forms it occurs 

 in the gland-cells, whose secretion is often grass- 

 green. In Nemertopsis peronea, on the other hand, 

 the pigment is confined to the interstitial cells, which 

 form two long dorsal stripes of red-brown colour. 

 Burger describes numerous instances of protective 

 coloration and of marked colour - resemblances 

 between armed and unarmed forms found living 

 together. His figures show again the frequency of 

 bands both longitudinal and transverse, but I have 

 not been able to find any suggestions as to their 

 meaning or origin. The pigments also have not yet 

 been investigated. 



The remaining flat-worms, being parasitic, display 

 no brilliancy of colour. 



The Pigments of the Gephyrea 



In the small order of the Gephyrea known as the 

 Echiuroidea a very interesting pigment occurs. The 

 curious form known as Bonellia viridis is bright 



