SABELLARIA SPINULOSA. 17 



gland-cells, and now and then it assumes a clavate outline, and in the preparations a few 

 show a slight constriction below the tip. 



On each side of the posterior groove of the mouth with its glandular folds is a bifid 

 process, the anterior rounded portion of which is applied to the soft external fold of the 

 mouth, whilst the pointed and somewhat ligulate process projects, like a ventral branchia, 

 downward and slightly forward. These organs probably act in conjunction with the 

 posterior buccal groove in tube-formation. 



The body (Plate CXII, figs. 1 — 1 e) is somewhat flattened, marked dorsally and 

 ventrally by a red streak. The cuticle is delicate and iridescent dorsally between the 

 branchiae, and is ciliated, especially over the sites of the blood-vessels. The dorsal groove 

 over the buccal region is also ciliated. Transverse rows of very long cilia also occur 

 behind the stomach and produce currents directed anteriorly. The ventral surface is 

 likewise ciliated and aids in the driving of the current forward, the water being expelled 

 anteriorly by undulatory movements of the body. Ingoing and outgoing currents are 

 visible at the mouth of the tube (Arnold Watson). 



Arnold Watson has observed that the contents of the lar^e muscular or^an or 

 gizzard (Fig. 139, pv.) at times receive careful treatment before passing into the intestine, 

 sometimes being forced into the dark part of the adjoining oesophagus, or into the first 

 part of the intestine, but returned to the gizzard for further treatment. 



On the ventral surface opposite the second and third segments is a smooth ovoid 

 area clearly differentiated from the surrounding parts by an elevated border. 



Arnold Watson finds that the peristomial membrane is less developed than in 

 S. alveolata, and thus the median cirrus is able to hold its own. 



The firm cylindrical region, which splits in front to form the two pillars of the 

 crown, has at its posterior border several processes, which apparently pertain to the next 

 segment. 



Dorsally (Plate CXII, fig. 1) is a pair of branchiae of the normal shape, and from 

 them a fold passes ventrally on each side, a space, however, intervening between it and the 

 outer limb of the bifid postoral process. At the end of this ridge is a broad, flattened, 

 pointed lobe or papilla, and sometimes two occur. Such would appear to indicate the 

 first foot of the anterior or thoracic region of the body, more especially as on each side 

 of the mid-dorsal groove a tuft of three long simple bristles (Plate CXXIII, fig. 2 c), with 

 striated shafts and translucent tapered tips embedded in the tissues, passes forward to the 

 anterior crown. The inner bristle on each side forms a pair with its neighbour, and the 

 tips are slightly incurved towards each other ; the second and third (outer) are smaller. 

 These bristles pass forward in a nearly parallel manner, only very slightly widening in 

 front. The most interesting feature, however, is the occurrence to the exterior of these, 

 also embedded in the tissues, of several types of the modified bristles in the paleal 

 crown. Thus the slipper-shaped kind with the shaft coming off at an angle, the form 

 resembling a broad and short bill-hook, and the broad paddle-like external paleas with 

 the lateral spikes and special central process,, are each represented on one side or 

 the other. 



Mr. Watson notes that in the first segment the bristles are on the dorsal side of 

 the cirrus, the latter being between them and the building organ. In the second the 



172 



