CAPITELLIDjE. 



271 



included in the great dorsal. Certainly no oblique muscle between the two latter appears 

 as a proof of a contrary view. All the muscles are covered by a comparatively thick 

 myolemma. Anteriorly there are two median ventral longitudinal muscles of a somewhat 

 elongate shape, the narrow end being external, whilst the inner is curved on each side to 

 form a hollow below the nerve-cords, which are ovoid in section and with a single neural 

 canal. They lie in the area above the muscles and below the transverse band to which 

 the mesentery from the alimentary canal is fixed. From each side of the nerve-cords at 

 intervals a large nerve passes outward, and bending down between the central muscle 

 and the adjoining, are certain of its fibres passing to the lateral region of the body as well 

 as supplying twigs to the muscles themselves. Vertical muscular fibres from the ventral 

 border also pass upward at the sides of the central muscle to the edges of the median 

 dorsal muscles. The nerve-area lies freely on the summit of the muscle surrounded by a 

 firm neurilemma. A single neural canal occurs in the middle superiorly, but it is much 

 less than that found, for instance, in Notomastus Grubei of the ' Challenger.' 



-.Orrv. 



Fig. 130. — Transverse section of the anterior region of Capitella cajpitata. ov. Ova. vd. Accessory gut. 



In transverse section the body-wall of Capitella capitata (Fig. 130) has under the 

 cuticle a thick layer of hypoderm, which Fischer 1 calls the matrix of the cuticle, and the 

 basement-tissue. Beneath is a well-developed circular layer of muscular fibres, which in 

 the mid-ventral line passes external to the nerve-cords. The dorsal longitudinal muscles 

 are separated only by the mesentery suspending the gut in the middle line, from which 

 they extend as a continuous muscle on each side to the region of the oblique (called by 

 Dr. Eisig the transverse). Their lower borders are thickest. The ventral longitudinal 

 muscles, though somewhat shorter in total length, are more massive, but taper a little 

 on each side of the nerve-cords to which they closely approach. The oblique muscles 

 pass from each lateral region and are inserted over the nerve-cords, the circular muscular 

 coat curving upward to form an arch immediately over the cords. These muscles are of 

 considerable strength, and when contracted they cause the ventral region of the body 

 to be grooved, a large rounded area projecting on each side. Fixed to the sheath of 

 the oblique muscles in the female is the ovisac containing large ova. The ventral gut 

 (Nebendarm) has thick muscular walls, and is closely adherent to the upper alimentary canal. 

 The dorsal mesentery attaches the gut superiorly. The ciliated intestinal groove carries 

 the water forward from the vent. The nerve-cords are distinct between the ganglia, and 

 have only basement-tissue, hypoderm, and cuticle externally. A neural canal lies in the 

 1 i Anatomische-histol. Untersuch. von Capitella capitata/ Marburg, 1884, p. 12. 



