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 McIntosh’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 
