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Transactions. 



tinuous collar (fig. 3) ; but the chaetae are in reality in four distinct fan- 

 shaped groups, two on each side, which touch one another ; though the two 

 dorsal and two ventral groups are separated slightly in the median lines. 

 Each group is contained in its own chaetophore, the lips of which project 

 slightly beyond the collar, as a dorso-ventrally extended fold, parallel with 

 its margin. The bases or roots of each of the four bundles of chaetae can 

 be seen converging as golden lines within the collar to a point deeply 

 removed from the margin. 



These chaetae are not of uniform length, those on the sides being longest, 

 those on the ventral being shorter than the dorsal ones. The chaetae are 



d— 



Fig. 4. 



Fig. 3. 



Fig. 3. — JSide view of the anterior end of F. bicolor (enlarged). The surrounding 

 jelly is not indicated, a, the tip of the palp (or subtentacle of Ehlers) ; 



b, tips of a few of the tentacles ; c, dorsal bundle of peristomial 

 chaetae; d, ventral bundle; e, median dorsal tentacle, or "lingula"; 

 /, peristomium (the " chaetigerous lamella" projects beyond its edge); 

 g, the 1st chaetigerous segment ; h, the 3rd chaetigerous segment, 

 bearing the hook in the ventral lobe of the parapodium. 



Fig.' 4. — View of the head from above, after the removal of the cephalic crown 

 of bristles ; the palps are cut across, and on the right side of the figure 

 the groove along its ventral surface is represented, a, the palp ; b, the 

 tentacular platform from which the tentacles have been removed ; 



c, the peristomial chaetigerous lamella bearing the bases of the bristles ; 



d, the median dorsal tentacle, or " lingula " ; e, the cerebral region of the 

 prostomium, with pigment spots. 



so closely placed at their origin from the chaetophores that they touch 

 one another, and form a palisade through which it is almost impossible to 

 see the enclosed tentacles and palps. The dorsal gap is wider than the 

 ventral, except in very much contracted specimens, when the right and 

 left groups overlap ; but in less contracted condition the dorsal median 

 tentacle projects through this gap as a tongue-shaped organ, or " lingula." 

 At other times it may be found upright within the crown of chaetae. When 

 this cephalic crown is pressed aside or cut away the organs of the head 

 are exposed. 



The tentacles, or branchiae, are numerous delicate filaments, densely 

 crowded together in two dorsal groups, one on each side of the middle 

 line. They are shorter than the palps, which are about three-quarters 

 the length of the cephalic crown. Each group contains about 50 tentacles, 



