506 F. W. GAMBLE AND J. H. ASHWORTH. 



The Nnclial Organ. — The general appearance of this 

 ciliated groove has been described in the section (pp. 439, 440) 

 dealing with the external chai'acters. It is a single, curved, 

 narrow depression of the prostomial epidermis, and corre- 

 sponds to the pair of grooves in Maldanids, and to the pair of 

 eversible " Wimperorgane '' in Capitellids and Opheliidse. 

 The epithelial cells which line it are of different kinds. 

 Some are secretory, others sensory, many are ciliated, and 

 these are the only ciliated cells which occur in the epidermis. 

 At their bases the epithelial cells are continuous with the 

 ganglion cells of the posterior brain lobes. 



The Eyes. — These structures were discovered in larvae 

 and post-]arv£e of A. cristata by Wilson (1882-3), but 

 they have only been recently re-described by Mesnil (1897) 

 in specimens of what the author considered to belong to the 

 genus Clymenides, Clap. More recently he has entirely 

 given up this conclusion, and has referred his specimens to 

 species of the genera Arenicola and Branchiomaldane. 

 We are able to show that eyes of an extremely simple struc- 

 ture occur in the post-larvae of three species of Arenicola, 

 and in the adult stages of all species. 



In the only trustworthy embryological account of Areni- 

 cola (the paper by Wilson on A. cristata, 1883) two eyes 

 appear on the prostomium when the larva is only a day old, 

 and they persist up to the latest stage that Wilson obtained 

 (fifteen days old, with six chaetigerous segments). In 

 sections of a Jamaican specimen, 7*5 mm. long, we can still 

 see embedded in the anterior brain lobes several eye-specks, 

 each consisting of a mass of brown spherical pigment granules 

 arranged round a clear central body which projects anteriorly 

 somewhat like a lens. The structure of these organs is not 

 well preserved. 



In A. marina (PI. 24, fig. 34, Oc.) there are, during the 

 post-larval stage, four to five eyes on each side of the prosto- 

 mium embedded in the ganglionic layer of the brain. They 

 measure '008 mm. in diameter, and consist of a cup-shaped 

 mass of brown pigment granules partially enveloping a clear, 



