183 
posed of a cup-shaped mass, about ‘01 mm. in diameter, 
of reddish brown pigment spherules, grasping the base 
of a spherical or ovoid lens. 
The animal is sensitive to light. If its anterior end 
be protruding from the burrow and light be thrown upon 
it, the worm at once disappears from view. In its re- 
action to light Arenicola resembles the earthworm, and, 
as in the latter, the re-action may be due to the general 
sensitiveness of the anterior end. 
The Prostomium (figs. 5, 47 and 48).—The epithelium 
of the anterior and dorsal face of the prostomium consists 
of columnar cells among which slender fusiform sense 
cells may be distinguished. These are generally in small 
groups and their slender tips are level with or project 
slightly beyond the outer surface of the cuticle. The 
bases of the cells are in intimate relation to either the 
cells of the brain itself or to the fibres of the nerves which 
connect the epithelium to the brain. In some prepara- 
tions the neurofibrille traversing the sense cells may be 
seen. Among the ordinary columnar cells of the pros- 
tomial epithelium there are, especially in the mid-dorsal 
region, numerous swollen gland cells. 
DEVELOPMENT. 
The early stages of development of Arenicola marina 
are unknown. <A brief resumé may be given of the 
development of A. claparedi. We may presume with 
moderate certainty that the development will follow 
similar lines in the two species.* 
* The following account is from observations made during my 
occupancy of a Table in the Zoological Station in Naples, in April, 
May and June, 1900:—From April 7th onwards specimens of 
A. claparedit were examined at frequent intervals, and on April 21st 
the first ripe males and females were obtained, the eggs fertilised, and 
the early stages of segmentation observed. The observations on the 
