26 SABELLARIA ALVEOLATA. 



of the blades touch the bases of the outer palese and form a very regular second row, the 

 two sides making an ovoid area. 



The inner or third row of the pale golden palese forms an oblique palisade, which 

 leaves only a narrow ellipse between them, and in lateral view, in Neapolitan examples 

 especially, the palisade shows a high dorsal margin and diminishes gradually to the 

 ventral edge. The typical palea (Plate CXXIII, fig. 3 6) has a long, flattened, tapering- 

 terminal blade, from which the shaft passes off at an oblique angle and tapers to a point, 

 the heel or shoulder being at the front edge, the outline of which is very slightly concave, 

 and with serrations on the margin. The dorsal outline presents a slight convexity in the 

 region corresponding to the arch of the foot. The transverse or slightly oblique strias 

 pass from the inner outline to the free edge where the notches are. The rest of the tip 

 is longitudinally striated. 



By rendering the tissues transparent Arnold Watson 1 has shown that in each 

 opercular lobe there are two setigerous sacs running longitudinally, the outer supplying 

 the outer paleas, the inner furnishing the median and inner palese which lie alternately 

 in the sac. The developing palea3 originate as minute, angular particles (cells?), and 

 the more advanced travel through the tissue in a somewhat spiral fashion to reach their 

 positions at the dorsal end of each opercular crescent. Thus new palese take the places 

 of those which are injured or shed. The same observer counted the palese in a large 

 example about 2 inches in length ; thus in the outer row on the left thirty-five 

 occurred, besides one just coming into view, thirty-six on the right and one just 

 visible; in the median row twenty-four on the left (three unpaired) and twenty-five 

 on the right, whilst the inner series consisted of twenty-one on the left and twenty on 

 the right. 



The same author has carefully investigated the physiology of the lower lip, his 

 building organ, as shown in the accompanying sketch, the strands of muscle radiating 

 from the posterior border being noteworthy (Fig. 138). 



The dorsal arch of the mouth (Plate CXII, fig. 4 a) is of a deep purplish-brown hue, 

 and it passes backward till it meets with a buccal collar which joins its fellow of the 

 opposite side ventrally in a slightly spout-shaped margin. From the dorsal edge of this 

 collar springs a tapering buccal tentacle on each side. External to this collar ventrally 

 another dark brownish-purple and frilled lamella, considerably thinner than the former, 

 extends to meet that of the opposite side, so as to form another spout-shaped process — as 

 it were ensheathing the former, and connected externally with the inner base of the 

 bifid organ which guards the spout-shaped aperture ventrally. The bifid organ springs 

 by a broad base from the peristomial region, the massive and larger division curving 

 inward to meet its fellow in front of the external spout-shaped aperture, the chink of 

 which is observed between them. The anterior end of each is blunt and rounded, and the 

 dorsal surface is tinted brownish. The other process springs about midway from the 

 outer edge, and passes forward and outward as a short conical process in the Neapolitan, 

 but as a process with a longer filiform tip in the English examples, though its condition 

 is subject to variation. Moreover, on a long papilla on the dorsal edge of the base (that 

 is, behind the external pointed papilla), a row of fine bristles projects, the long axis of 



1 'Rep. Brit. Assoc./ 1910 ; p. 034. 



