192 POLYDORA. 



Numerous clavate (thecate) Infusoria occur on the dorsum and on the branchise, whilst in 

 the intestine are many Gregarines. 



Habits. — This species occupies a tube of dense, translucent, chitinous material coated 

 with sand-grains, and it is interesting to note how neatly the black grains, for instance 

 in those from White Cliff Bay, Isle of Wight, are intermingled at intervals with the pale 

 grains. In those from Cobo Bay, Guernsey, fragments of shells are largely used with the 

 sand-grains. At St. Andrews the sandy tubes in the fissures of the rocks occur in 

 association in considerable numbers. When placed in a vessel of sea-water little is seen 

 of the inhabitants, which are somewhat shy. By-and-by, when all is still, two slender 

 filaments like hairs (the tentacles) are protruded, and they make extraordinary move- 

 ments, coiling, wriggliug, and twisting most actively, and yet with a definite purpose, for 

 grains of sand and particles of various kinds are drawn or mysteriously passed to the 

 mouth of the tube to repair damages or lengthen it. These mobile sensitive filaments 

 stretch a long distance and grasp and pull particles toward the aperture. A minute red 

 streak along their centre indicates the vascular supply. When removed from its tube it 

 is an active and restless form, lashing its tentacles in the water, and coiling or bendino* its 

 body in ceaseless movements. Occasionally an injured animal will remain at rest for a 

 short time, but this seldom occurs in a free uninjured one. 



This was one of the forms which the acuteness of Claparede (1863) rescued from the 

 confusion of forms associated with Spio. 



Pygospio seticornis, (Ersted (non Fabr.), Mesnil 1 thinks is Cunningham and Ramage's 

 species in ' Trans. Roy. Soc. Bdinb.' 



Mesnil (1896) found irregular segmentation in one example, the fifth left corre- 

 sponding to the fifth and sixth segments on the right, and occasionally the winged hooks 

 do not occur till the ninth segment. 



Genus CII. — Polydoea, Base, 1802. 2 



Prostomium generally bifid, though occasionally rounded in front, and from this a 

 prominent ridge passes backward for a few segments. Eyes two pairs, or absent. Peri- 

 stomium projects at the sides and in front, and bears two long tentacles, each with a 

 papillose and ciliated groove, and the mouth forms a V-shaped aperture ventrally with 

 two prominent rounded lips. Body generally translucent, of small size, conformable to 

 that in the Spionidae ; segments numerous, reaching 200 or more, generally furnished 

 with double groups of bristles dorsally and ventrally in front, but about the seventh the 

 ventral division bears winged hooks. Anterior region of few segments. Branchiae 

 generally begin after the sixth bristled segment (except in one form), and they vary in 

 number. The fifth bristled segment is of great length, has dorsal and ventral capillary 

 bristles, but also highly modified large hook-like bristles accompanied by lancet-like forms, 

 and the ordinary hooks appear on the sixth or seventh segment and continue to the 

 posterior end. Body terminates posteriorly in a cup-like caudal appendage or funnel. 



1 'Bull. sc. Fr. Belg./ xxx, p. 85, 1897. 



2 ' Hist. nat. des Vers/ i, p. 150, Paris, an x. 



