146 
Epidermis: Pigment. 
There is a well-developed cuticle formed by the 
mucus cells of the epidermis. 
In adult specimens the skin of the anterior and 
middle portions of the animal is sub-divided by grooves 
into a series of squarish, oval or polygonal areas 
(fig. 5). These are ‘composed chiefly of large club- 
shaped mucus cells and of elongate columnar cells, many 
of which are almost filled with pigment granules, 
especially in old specimens. These granules, which are 
dark yellow or brown when viewed singly, but nearly 
black in the aggregate, are more abundant in the distal 
part of the cells, and give to many of them a clavate 
appearance. Pigment cells are present all over the 
epidermis, extending on to the prostomium, but are less 
numerous in the nuchal organ than elsewhere. The 
epidermis in the grooves between the raised areas is com- 
posed of shorter cells, in which the pigment is present 
in less quantity and mucus cells are wanting. 
In the tail the epidermis is raised into rounded 
papille (see above) the structure of which corresponds to 
that of the raised areas described above. 
Sensory cells are also present in the epidermis, being 
specially abundant in many of the grooves. 
When specimens of Arenicola are handled a yellowish 
or greenish pigment exudes from the skin and stains the 
hands. This, which is readily soluble in alcohol, and to 
some extent in sea-water, is probably a lpochrome. 
There is also a brown or black pigment, the fine granules 
of which are insoluble in alcohol, and are readily seen in 
sections, especially of old specimens. According to 
MeMunn (Q.J.M.S., Vol. 30, p. 74), this pigment 
resembles melanin in its resistance to solution, and he 
