SEA-FISHERIES LABORATORY. 263 



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 neurohbrilhe 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 resume may be given of the 

 development of A. clajyaredii. 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. claparedii 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 



