196 POLYDORA. 



The Polydorids are a brittle group, throwing off their long tentacles, and readily 

 rupturing the body. 



They perforate shells and rocks of various kinds. 



Inhabit tubes of sand or burrows in rocks and shells. 



Martin Slabber 1 (1778) gives a figure of " Scolopendra marina" which is evidently a 

 Polydora, probably the common species, though the differentiation of the fifth segment and 

 other parts is not alluded to. The cilia on the branchiae, the posterior funnel, and the 

 capillary dorsal bristles are indicated. 



The Spio seticornis of De Blainville 2 (1828) is represented on Plate XIX, fig. 2, and 

 so far as can be observed it is a Polydora with four bristled segments in front of the fifth 

 with its great crotchets. He placed Spio and Polydora with Pectinara and the Serpulids 

 under his first order, Heterocriciens. 



Ouvier (1817) appears to have confounded this form with Spio, for he figures the 

 anterior region of Polydora as that of Spio seticornis, though he describes the genus Spio 

 as different from the Polydora of Bosc. 



Audouin and Milne Edwards (1834) thought that Polydora might be placed amongst 

 the Nereidiens, and that in general form it approached Peripatus. They do not allude to 

 its tentacles. 



GErsted 3 followed Johnston in giving the name Leucodorum to the genus, which he 

 placed under his Ariicias naidinae, a sub-division of the Ariicise verse. He mentions two 

 species — L. ciliatum, Johnston, and L. coecum, GErsted. 4 



M. de Blainville thought Baster's figure (Opuse. subs. II, LIV, IK, Plate XII, fig. 2) 

 had a resemblance to that observed by Suriray, and represented in the " Atlas du 

 dictionnaire " under the name Spio seticornis (Plate XIX, fig. 2). It appears to be 

 Polydora. Slabber's Scolopendra marina is similar. 



De Quatrefages 5 (1850) observes that in Polydora the ventral vessel is single 

 throughout the greater part of its extent, but in front it bifurcates, and the three 

 anterior rings have a double vessel. The dorsal trunk presents an inverse arrange- 

 ment, for it is single in the four anterior segments, then bifurcates and forms the ventral 

 trunks. The dorsal and the ventral trunks are joined by large connecting branches. 

 The branchiae have a central canal and lateral lacunae, with cilia on the surface, and 

 De Blainville thought that the tentacles were also respiratory, their canal communicating 

 with the general cavity of the body. 6 



The Nereis contorta of Dalyell 7 (1853) may be a Polydora to judge from the sucker-like 

 posterior extremity, but he mentions no differentiation of the fifth segment. Of the Spionids 

 he observes that one is extremely rare, and the other so minute as readily to escape 

 observation. It is otherwise now. It is possible that his Spio seticornis may be Pygospio. 



1 ' Naturkundige Verlustigungen/ Haarleim. 

 3 'Diet. Sc. nat./ t. lvii, p. 441. 



3 < Arch. f. Naturges./ Bd. x, p. 105, 1844. 



4 Mr. Southern records Polydora caeca as common on the west coast of Ireland. ' Proc. Roy. Irish 

 Acad./ vol. xxxi, no. 47, p. 103, 1914. 



6 ' Ann. Sc. nat./ 3 e ser., t. xiv, p. 282. 



6 Ibid., p. 293. 



7 ' Pow. Creat./ vol. ii, p. 156, pi. xx, figs. 19 and 20. 



