354 SERPULA VERMICULARIS. 
fang, a sinus, and a prominent prow beneath it ; posterior outline slightly concave, inferior 
outline convex. Posterior hooks smaller, but with five teeth above the chief fang. Tube 
3—4 inches long, having a trumpet-shaped aperture, pinkish or greenish in colour, with rings 
of growth, and occasionally a rough ridge ; spirally coiled posteriorly. Free or fixed. 
The body-wall anteriorly in Serpula vermicularis (Fig. 167) has externally a somewhat 
firm hypoderm, and ventrally it is more vascular. The circular muscular coat extends all 
round and has special developments at the feet. The dorsal longitudinal muscles form 
massive kidney-shaped lobes in transverse section, separated in the mid-dorsal line, but 
extending from the dorsal almost to the ventral edge, and are proportionally larger than in 
Protula. ‘The ventral longitudinal muscles, again, are smaller, widely separated, and have 
the nerve-cords with the large neural canal at the imner border. Between the latter 
Fic. 167.—Transverse section of the body-wall of Serpula vermicularis, in the anterior region. d., alimentary 
eanal; dm., dorsal longitudinal muscles; m., special ventral longitudinal muscular layer; nc., nerve 
cord; ne. (vight), neural canal; vi., ventral longitudinal muscles; wv., ventral blood-vessel. 
stretches a thin but continuous layer of longitudinal fibres, having the circular coat 
externally and the ventral blood-vessel internally. The dorsal fold (external) at the foot is 
hollow in the centre. A peri-intestinal sinus envelops the alimentary canal throughout the 
ereater part of its length. The thoracic glands are similar to those in the Sabellide. Little 
change occurs in the structure of the body-wall posteriorly. In this region the nerve-cords 
are in contrast with the large neural canals, since in section the nerve-tissue proper 
is barely a fourth the area of the neural canal. It thus appears to be misleading to 
term the canal a “giant fibre.” The remarkable intermingling of the muscular fibres which 
course from the dorsum by the side of the alimentary canal and pass below the ventral 
blood-vessel to cross with fibres from the opposite side and reach the circular coat is one of 
the features of the region. 
SYNONYMS. 
1555. Vermes in tubulis delitescentes, Rondeletius. Univ. Aquat. Hist. pars altera, p. 110, with fig. 
1606. Tubul alii paruit in quibus etiam vermes delitescunt, Aldrovandi. De reliq. Anim. exang., 
p. 562, with fig. 
46. Serpula vermicularis, Linneeus. Fauna Suecica, p. 280. 
55. Tubus 3 Hillis. Corall., p. 117, pl. xxxvini, fig. 2. 
58. Serpula intricata, Linneeus. Syst. Nat., 10th Edit., p. 787. 
5 contortuplicata, idem. Ibid., 10th Edit., p. 787. 
