34 AMPHFCTENID^E. 



dissepiment. Branchiae two pairs, on the second and third segments/ pectiniform, 

 lamellae diminishing from within outward and attached to a tapered basal stem — often 

 coiled, situated near the feet. Anterior heart connected with peri-intestinal sinus. 



Bristles commence on the sixth segment, arranged in two series, viz., three in the 

 first region and twelve to fourteen in the second, the latter stronger, and accompanied 

 by lamellae for hooks. The structure throughout is the same, viz., strong, simple, tapering 

 bristles with traces of wings on the tips, and a shorter series with spear-like dilatations at 

 the end of the shaft, and a tapering, hair-like tip. Some forms have hooks with long 

 shafts anteriorly (Hessle). Pectiniform hooks, commencing on the ninth segment, and in a 

 single row (Hessle). Bristle-like hooks (probably ventral, though in young dorsal — Hessle) 

 on each side of the base of the caudal appendix (scapha). Tube free, tapered, nearly straight 

 or very slightly curved, composed of neatly arranged sand-grains and secretion, or in one 

 genus of fragments of shells. Feet reduced as in all tubicolar forms. Nerve-cords 

 comparatively free. Tentacles innervated from the anterior ganglia (Nilsson), from the 

 middle ganglion (Hessle), the former homologising them with the palps. Nerves for 

 tentacular membrane from the middle ganglion. Nuchal organ, as in the Ampharetidae, 

 raised (Hessle). A groove between tentacles and mouth. 



In the Amphictenidae Schneider found a heart-body, and Cunningham 2 (1888) 

 mentions that an anterior heart is present, and is connected with a blood-sinus on the 

 walls of the intestine. 



Some authors, like Eisig and Picton, think the heart-body equivalent to the chlora- 

 gogenous coat of the vessel pushed in. Picton considered it mesoblastic in Polymnia, and 

 analogous to the liver of vertebrates, but glycogen is absent so that its complete analogy 

 is not proven, though other products may be present and stored. The functions of the 

 pigment and the chitinous bodies are unknown. It has been suggested that waste 

 products may be carried through the heart-wall and thence to the nephridia and leucocytes. 

 Beddard and Horst, again, are of opinion that the heart-body is hypoblastic. Eisig 

 views it as modified peritoneal tissue, though Schaeppi has found it of different chemical 

 composition. It is in the blood-stream as the liver is, and hence Fauvel considers it hepatic 

 in function, and that it has no connection with amoebocytes. Its occurrence in so many 

 families of Polychaets is noteworthy, for besides the Amphictenidae, it is present in the 

 Opheliidae, Chloraemidae, Cirratulidae, Ampharetidae and Terebellidae, whilst in the 

 Arenicolidae it is paired, and unites the gastric plexus with the ventral. Functionally 

 some are inclined to the view that it prevents regurgitation. 



In the anterior region of Gystenides hyperborea, Malmgren, the cuticle is tough, but 

 the hypoderm is comparatively thin. A thin circular muscular coat lies beneath the 

 basement-membrane. The dorsal longitudinal muscles are elongated in section, stretching 

 from the feet at each side to the dorsal middle line, where they are connate. The ventral 

 longitudinal muscles are thicker, but have a wide space between them occupied by the 

 transverse muscle formed by the circular coat augmented by other fibres. The nerve- 

 cords form an ovoid mass in section above the transverse muscular fibres, and there is 



1 According to Nilsson, the fourth and fifth segments. 

 Quart. Journ. Micr. Sci./ n.s., vol. xxviii, p. 261. 



2 ( 



