326 



PRAXILLBLLA GRACILIS. 



of the main fang, and in the rudimentary condition of the spikes on the crown ; all these 

 features with the comparatively narrow distal region being conspicuous in those of the 

 first bristled segment (Plate CIX, fig. 12 a). The main fang leaves the neck at more than 

 a right angle and its distal outline is sinuous so as to resemble a foot ; further a slight 

 swelling occurs on the throat at its base. In these segments (three anterior) the bristles 

 and hooks are in front of the boundary of the anterior third, and lateral in position. The 

 fourth segment is equally glandular, though short, and its row of hooks is longer. The 

 shafts of the hooks still retain their great length and curvature, increasing in size from 

 the somewhat slender basal region to the broad shoulder, then contracting at the neck, 

 which slightly widens in its passage forward to the crown. The main fang comes off more 

 nearly at a right angle than in the anterior feet, is proportionally less, is evenly curved on 

 its distal margin, and has four teeth on the crown above it. Moreover, the gular bristles 

 spring from the throat immediately beneath the great fang, curve forward to its tip, and 



m. 



Fig. 134. — Transverse section of Praxillella gracilis, ov. Ova. hyp. Hypoderm. 



bend upward above it. The distal region has straight strise superficially at the end, 

 oblique striae in the deeper part of the neck, and the shaft is longitudinally striated. The 

 hooks remain for the most part similar in the fifth, sixth, and seventh segments, except 

 that in some a tendency to differentiation of the crown with its four smaller teeth and the 

 trend of the posterior outline is observed. The typical hook shows a narrower neck above 

 the prominent shoulder, a shorter distal region or neck, which is broad at the crown and has 

 at least five (six, Arwidsson) teeth above the main fang, but the gular bristles retain their 

 position close to the base of the great fang, and without differentiation of the outline. The 

 hooks of the small form from St. Magnus Bay have a higher crown than those from 

 Canada. 



The posterior hooks, for instance those of the last row, differ chiefly in their smaller 

 size, the shafts being shorter, the smaller main fang, and the more prominent condition of 

 the crown with the smaller teeth, four of which are evident as in front. The gular 

 bristles have the same arrangement. The bristles of this region retain the structure of 

 those in front. As a rule the number of the hooks increases at the fourth segment, and at 

 the sixteenth there may be sixteen or seventeen in each row (Arwidsson). The same 



