POLYMNIA NEBULOSA. 135 



circular, anteriorly over the swollen thoracic region. Two circular bands occur in each 

 segment, whilst the longitudinal are in numerous separate strands, which give the dorsum 

 a corded appearance. 



Two varieties occur, viz., the large littoral form from Lochmaddy, and those from 

 deep water, which are smaller. 



Commensals. — In North Uist, as at Lochmaddy, Polynoe scolopendrina of large size 

 is frequently met with in the tubes of this Terebellid. It is hard to conjecture how the 

 soft— almost semi-gelatinous — annelid tolerates the stiff, hard-spined Polynoe, but it 

 shows no signs of uneasiness or injury, and the Polynoe must supply itself with food either 

 independently or from the catering of the Terebella. Very rarely was this commensal 

 found in the numerous examples procured from the Channel Islands (Guernsey and Herm), 

 and thus they were in contrast with those from Lochmaddy. Nor was a Polynoe found in 

 those from Scalloway. 



The tube 'of this form is composed of small stones, fragments of shells, or in certain 

 cases, as in Ireland, fragments of slate with secretion, and it is loosely bound together, 

 the cement readily giving way on attempting to remove it from its site. Some of the 

 tubes are three-quarters of an inch in diameter, and they may be in the form of a long 

 arch on a stone or rock ; the annelid, taking advantage of the surface of the stone, thus 

 saves both labour and materials. The tubes occur in some cases in groups or small 

 colonies on congenial sites. The tube of one from Valentia Harbour is composed of 

 fragments of leaves and other vegetable structures and fibres, the whole forming a 

 soft tube. 



An excellent account of the formation of the tube in confinement is given by De St. 

 Joseph (1894). This author also states that in dredged examples the general colour is 

 cinnamon with numerous white points, and thus corresponds with the so-called Terebella 

 MecJcelil. He mentions the occurrence of a papilla under the second pair of branchia3, and 

 the same on the iiYe succeeding segments between the setigerous process and the torus. 



Habits. — When seized in its tube it often breaks itself behind the bristled region, the 

 "suicidal mark" of the Terebellids. Few species, indeed, are more irritable, for when 

 touched it breaks off the posterior region, and almost always does so, even when cautiously 

 lifted. Yet it swims actively when placed in water. It is not luminous. 



Reproduction. — Eay Lankester 1 (1873) during the winter at Naples found the 

 eggs in abundance, and observes that " a delicate chorion forms round the egg after 

 segmentation, on the surface of the cleavage-cells, which are densely ciliated," and that 

 " the cilia were really processes of the protoplasm of the cells " and could be drawn 

 through the chorion, which they perforated. 



Lo Bianco (1909) found that the period of reproduction at Naples, where the species 

 is termed " Terebelle," was between August and May, most, however, occurring between 

 January and April. The yellowish-orange ova are enveloped in a gelatinous matrix 

 2 : — 4 cm. in diameter (fissato sull' orlo del tubo). 



A careful account of the development of this species was given by Milne Edwards 

 in 1844. 2 



1 Vide p. 100. 



2 Vide p. 96. 



