208 POLYDORA FLAVA. 



segments behind, and then diminish. They appear to be about thirty-five to forty in 

 number. Long cilia occur on them. 



In an example from Lochmaddy a large hook-like bristle of the fifth segment had its 

 tip apparently in process of reproduction, and it somewhat resembled in this condition 

 the hook-like bristles of P. Mesnili. 



In the alimentary canal of those from Guernsey are numerous Gregarinas of a short, 

 thick outline. 



A feature of moment occasionally observed on the surface of the Lithothamnion from 

 Guernsey is the fact that from the rounded aperture a curved groove proceeded some 

 distance and then ceased. Its depth would correspond to about half the diameter of the 

 body of the annelid, and, all things being taken into consideration, would be most easily 

 explained by the action of a solvent secreted on the body of the worm when applied to 

 the surface or from constant friction ; but, of course, this is conjectural, and the fact that 

 P. ciliata bores as readily in aluminous shale shows that other agencies must be con- 

 sidered. 



The surface of the Lithothamnion is dotted over with minute apertures, some of 

 which are in pairs, but others, generally a little larger, are not. The smooth surface of 

 the alga does not show the tubes of sand and mud so characteristic of the perforations 

 of P. ciliata in shale and sandstone. 



On April 21st an example discharged a quantity of yellowish ova in its vessel — 

 each being about 0*09 inches in diameter. 



Claparede (1870) considered that the large bristles of the fifth segment represented 

 neither the dorsal nor the ventral tufts, since in P. Agassizii there exists a distinct ventral 

 tuft, whereas in P. antennata the reverse occurs, viz. the presence of a dorsal tuft. He 

 was apparently unaware of the presence of both dorsal and ventral tufts in P. ciliata. 



Mesnil considers that the morphology of the bristles in the fifth segment of this and 

 other species is as follows : — The dorsal tuft comprises superior dorsal bristles, the 

 abnormal (hook-like large bristles) as the posterior dorsal, the capillary which accompany 

 them as the anterior dorsal ; whilst the small ventral tuft he regards as the entire normal 

 ventral series. He places considerable weight on the presence of packets of fine bristles 

 included in the foot, and which are absent in P. caeca of Oersted, 1 and he therefore 

 separates the latter species, which (Ersted described as blind. Mesnil 3 found it (P. caeca) 

 not in muddy tubes like P. flava and polybranchia, but in tunnels in the calcareous alga 

 Lithothamnion. This form closely resembles P. flava, the branchiae commencing on the 

 same segment (eighth). At the forty-fifth to the fiftieth setigerous segment the anterior 

 dorsal bristles are altered, for the wing is absent, and they are stout, short, and pointed, 

 constituting a distinctive character of the species, which, however, is not given by 

 (Ersted. The great hooks of the fifth segment resemble those of P. flava. Mesnil also 

 states that the great fang of the winged hook has an angle of 60° instead of 45°, as in 

 P. flava. Moreover, he found a young example with four eyes as in the ordinary form. 

 It has only seventy to eighty segments. If this form is really distinct from P. flava it 

 should occur on the southern shores of Britain. 



1 ' Ccmsp. Annul. Danica/ p. 39, fig. 104. 



2 ' Bull. sc. Fr. et Be%./ t. xxix, p. 19, pi. xii, figs. 23—29. 



