28 



SABELLAEIA ALVEOLA.TA. 



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the filaments spring from the summit as a single row. The central axis is deeply stained 

 by methylene-blue (Arnold Watson). 



In spirit the buccal region still retains deep purplish- 



^ . brown pigment on the sides, especially external to the 



/ /, y tentacles and between their basal folds. It is terminated 



on each side posteriorly, as in S. spinulosa, by a fillet which 

 has a branch ia dorsally and a flattened and pointed lamella 

 with a minute bristle-tuft below it ventrally, the bristles 

 having proportionally stout shafts and tapering, closely 

 spinous tops. They appear to belong to the ventral 

 series. 



The long dorsal bristles in the complex region of 

 Sabellaria spinulosa are thus absent, only developing palea3 

 occurring towards its anterior margin . Whether the smooth 

 bristles to the exterior of the ventral mouth-lobes represent 

 their equivalent or otherwise is at present unknown, but 

 their absence dorsally is noteworthy. Meyer's view that 

 such represents the dorsal division of the first segment 

 of the body is thus not without basis, more especially as 

 the tuft of characteristic bristles shows that the ventral 

 division is also present. The dorsal bristles seem to be 

 well developed in Tetreres murata, Allen 1 ; the first branchia 

 with the fillet and the papilla on its anterior margin would 

 thus appear to complete the parts of the first bristled 

 segment. 



The body (Plate CXII, figs. 4 and 4 a) is massive, rather 

 flattened, grooved both dorsally and ventrally, gently 

 tapered, both when viewed dorsally and laterally, from the 

 anterior to the posterior end, and divided into two regions, 

 besides the long, flexible caudal tube, which appears to be 

 invariably curved ventrally in the preparations. Numerous 

 long cilia, set in transverse grooves, occur on the dorsal 

 surface of the worm, and create the strong current 

 which carries ova, sperms and other structures out of 

 the tube, as well as aids in the respiratory process 

 (Arnold Watson). The dorsum is occupied throughout 

 by the branchiae, the first three of which have broader 

 flattened bases and more slender tips than the rest— 

 which increase in length to the seventh or eighth, and 

 then gradually diminish posteriorly. Their structure corresponds with that in S. 

 spinulosa. The lateral region has the segment-ridges and the lamellae for the hooks, 

 the latter posteriorly projecting outward as long cuneiform processes, which Arnold 

 Watson observed to be moved freely backward and forward, as well as retracted. 

 1 Mourn. M. B. A./ vol. vii, p. 301, pi. x, figs. 1 and 3. 



Fig. 139. — Sketch of the alimentary 

 system of a young Sabellaria alveolata. 

 pc, cephalic plate ; th.gl., thoracic 

 glands; oss., oesophagus; ul., uncini- 

 gerous lamellae; pv., proventriculus ; 

 tng., anterior stomach ; mg'., posterior 

 stomach; br.gl., brown glands; int., in- 

 testine (after Arnold Watson). 



