494 



ARICIIDiE. 



Family XIV. — Arioiim], Audouin and Edwards, 1834. 



Head (prostomium) a pointed cone, with or without eyes, and devoid of processes. 

 Peristomial segment without appendages. Body tapered anteriorly and posteriorly, 

 flattened dorsally, rounded ventrally. Segments narrow. Proboscis a frilled rosette. 

 Tail with two long cirri. Feet dorsal in position, the ventral division being dorso-lateral 

 anteriorly and dorsal posteriorly. Branchiae ligulate, dorsal. Rows of papillae behind the 

 anterior feet. 



Bristles of several kinds — elongated and tapering bristles peculiarly serrated so as to 

 appear camerated, simple tapering bristles, or the bases of the stronger ventral serrated 

 forms modified by friction. 



The nerve-cords (Fig. 93) anteriorly pass from the ganglia to the ventral surface, 

 where they are at first widely separated, a broad band of transverse fibres intervening. 



Fig. 93. — Transverse section about the anterior third of Aricia Latreillii, Aud. & Edw. 



They lie outside the circular layer, and beneath and external to the oblique bands at the 

 inner edge of the ventral longitudinal muscles. Then the median space contracts, the 

 nerves approach each other at the inner edge of a somewhat triangular area of hypoderm, 

 the circular coat bending upward along the inner edge of the ventral longitudinal muscles 

 to the raphe on each side at the summit, to which the oblique muscles are attached. The 

 hypodermic area in this region is larger than it is posteriorly, and the surface is raised, 

 not grooved. By-and-by, however, a broad groove appears and then the narrow one 

 posteriorly. Toward the middle of the body the trunks have been pushed further 

 inward and are closely enveloped laterally by the ventral muscles, the fibres being bound 

 by a thin band of the circular muscle, which is intimately applied to the sheath of the area. 

 The latter is now somewhat clavate in outline (Fig. 94), springing by a slightly wider 

 base from the line of the ventral median groove, and marked by transverse fibres at the 

 base (externally) ; indeed, this narrower region below the cords is transversely streaked 

 throughout and has minute (stained) nuclei here and there. The cords occur at the 

 upper or inner dilatation, and are ovoid in outline, with a large neural canal in the centre 

 superiorly. Occasionally two smaller lateral canals are visible on the same level. Groups 



