ANATOMY AND CLASSIFICATION OF THE ARENTCOLIDJ:. 507 



solid-looking body which projects outwards. Similar eyes 

 are found in specimens of the common lugworm, 25 mm. long. 

 It is difficult to say whether they persist throughout life, 

 owing to the quantity of pigment in the prostomium increasing 

 with the age of the animal. 



In specimens of A. Claparedii (17 and 2G mm. long) 

 there are three to four eyes in the deeper parts of the 

 prostomial epithelium and between the ganglion cells of 

 the anterior cerebral lobes. The lai-gest measure '01 mm. 

 in diameter, and are provided with a layer of red pigment 

 granules. 



In A. Grubii and A. ecaudata we have obtained the 

 clearest preparations of the eyes. In a post-larva of the 

 latter species, 7"2 mm. long, there are about twelve eyes on 

 each side of the prostomium along the greater part of its 

 length. They were arranged in two linear series, one on 

 each side. Occasionally two eyes occur close together, and 

 one or two are placed nearer the median line than the rest. 

 The eyes measure "01 mm. in diameter, and consist of a clear, 

 lens-like structui^e pointing outwards and upwards : of a 

 transparent, less highly refractile central portion : and of a 

 hemispherical coat of sepia-coloured, rounded pigment 

 granules (PI. 27, fig. 63 a). 



The anterior eyes are placed in the nervous layer, imme- 

 diately below the epidermis and on the course of the nerves 

 given off from the front edge of the commissural brain to 

 supply the prostomium. Further back the eyes are sunk in 

 the ganglionic layer of the brain itself. 



In full-grown specimens of A. ecaudata (six to seven 

 inches long) the eyes are still present, and apparently more 

 numerous than in the post-larval stage. They measure "012 

 mm. in diameter, and are now partially surrounded by a red 

 pigment in the form of minute spherical granules. They 

 occur in the same regions as before, but are also found in the 

 median brain lobe which undei-lies the nuchal organ. 



In their simple form and deep situation the eyes of 

 Arenicola recall those of Mastobranchus (Capitellidse), 



