66 ARENICOLA MARINA. 



which in some assume the form of distinct areola, whilst the distal and larger area is 

 covered with smaller conical papilla), larger papillae again marking the aperture into the 

 oesophagus. In old specimens the region of the large papillae at the base is blackish, 

 whilst that of the smaller papillae is pale greyish-brown. Differences seem to exist as to 

 the extent of the surface covered by the large basal papillae. Ashworth l notes that in 

 examples from Vierville the papillae of the proboscis were large. The proboscis is followed 

 by the pinkish or greenish-brown oesophagus which pierces the three diaphragms, and just 

 behind the last bears a pair of glands (sacs). Behind is the stomach covered with yellow 

 cells and blood-vessels, and extending to the eleventh or twelfth bristles, after which is the 

 yellowish-brown or dark olive-green iutestine which terminates in the vent. The ventral 

 groove of the stomach is ciliated, and this groove extends to the anus Sand and muddy 

 sand are taken in by the proboscis and mixed with the oesophageal secretion, then it 

 receives the secretion of the two glands, passing on to the stomach. The movement of 

 the canal in this region is thought to favour the thorough mixing of the food and secretion 

 (Ashworth). The ventral groove, moreover, is in close relation to the sub-intestinal 

 vessels, and a thin cord of mucus is seen in fresh sand-casts. The species thus acts as a 

 cleanser of the sand from decomposing matter, for it is generally found only where sand 

 is thus mixed. 



The tail is without gills or feet. There may be seventy segments (Ashworth), but 

 the worm has a tendency to throw off the last few segments when irritated, new segments 

 being formed at the anterior end of the tail, where the segments are short, but posteriorly 

 they are longer, some having about ten annuli. Near the posterior limit of each segment 

 in the mid-tail region is an annulus larger and more deeply pigmented than the rest, and 

 apparently corresponding to the setigerous ring in front. A shallow groove occurring in 

 the mid- ventral line marks the position of the nerve-cord. 



Nineteen pairs of bristles occur along the sides, and they can be extruded a consider- 

 able distance on their papillae. The first pair is shorter and more slender than the 

 succeeding. In large specimens the bristles are about one-fifth of an inch in length, and 

 they are directed transversely outward. The shaft of these bristles (Plate CM, figs. 11 — 

 H a — c ) i s powerful, flattened, and finely striated. The terminal region of the bristle is 

 distinguished by the slight diminution at the commencement of the wing and it tapers 

 from this point to the tip. The wing (or wings, for two may be present) is narrow, forms 

 a web like the barbs on a feather, though from its structure it readily splits, widens and 

 again diminishes distally. As the bristle lies with the web on one side, the opposite edge 

 has only minute serrations for some distance, whilst the dorsum is smooth. Then this 

 edge becomes more spinous and spikes become evident on the dorsum. Gradually as the 

 wing diminishes in breadth the spikes increase in length and form whorls on the slender 

 tip. Though it may not be easy to distinguish the bristles of Arenicola marina from those 

 of foreign species they seem to be readily differentiated from those of Arenicola branchialis 

 and A. ecaudata — being larger, and with more coarsely spinous tips than either of the two 

 just mentioned. 



The bristles represent the dorsal division of the foot, the long hooks the ventral 

 division, and they are coincident with them. The first six tufts show a gradual increase 



1 ' Ann. Sc. nat./ 9 e ser., t. x, p. 112. 



