226 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



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 

 papillae (see p. 219) 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 iu alcohol, and to 

 some extent in sea-water, is probably a lipochrome. 

 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 

 McMunn (Q.I.M.S., Vol. 30, p. 74), this pigment 

 resembles melanin in its resistance to solution, and he 



