206 REPORT— 1851. 



The Terebellce differ from the SabellcB in the uniformly abdominal position 

 of the feet and rugae for the hooks. Since the tube \s fixed, this arrange- 

 ment entails no inconvenience. In another essential respect the Terebellca 

 are distinguished from the SahellcB. In the former the cephalic tentacles are 

 powerful manual appendages, uniting in themselves the threefold office of 

 touch, prehension, z^wA pulling \ for it was shown that through their aid the 

 animal assists the operation of the hooked and setiferous feet in drawing 

 itself forwards; in the Sahella, the cephalic appendages are quite incapable 

 of any, the slightest motive act ; they are exclusively branchial. The duties of 

 locomotion therefore in this latter genus devolve exclusively on the feet. 

 In the Terebella, the setiferous feet are limited to the anterior end of the 

 body ; the posterior presenting the form only of hook-armed ridges. In 

 Terehella nebulosa these feet amount to twenty-three in number; the setae 

 with which these feet are furnished, are simple or unserrated lancet-shaped 

 and flattened hairs. The feet themselves are capable of only slight extrusion 

 beyond the plane of the body, serving more the purpose of trowelling, 

 plastering, and polishing the interior of the tube, than of moving the animal 

 in its cell. The hooks (fig. 24'), in nearly all species of Terebellis, are disposed 

 in double rows on the dorsum of each ridge. This arrangement exists inva- 

 riably on the " ridges " of the posterior |^ths of the body ; on the anterior 

 setiferous portion they are often in single rows. It is evidently designed as a 

 means for ^rm\jfixitig to the tube the tail end of the body, in order that 

 upon it as a pivot, the anterior portion and the head may enjoy perfect free- 

 dom of motion. Considering the extreme power of elongating and contract- 

 ing the body with which these ornamental worms are gifted, it is mechanically 

 clear, that upon such a basis a great range of movement is secured. The 

 hooks themselves are furnished with one long and large tooth, and several 

 smaller ones above the former ; the back presents a projecting spine, to which 

 a tendon is attached, the office of which is to /<ngrasp or loose the tooth from 

 its hold, and which may be called thelaxator hamuli. The attached conical 

 base of each hook is furnished with another tendon, the muscle of which may 

 be called the tensor hamuli, as through its agency the act of ^a:m^ the hooks 

 is performed. On the ventral median line in Werehella nebulosa thick muscular 

 transverse scale-like rugae, mistaken by Montagu fur actual scales, are de- 

 veloped, forming in part afulcrumfor muscularaction,andin part steadying the 

 cephalic end of the body, with a view to the pulley-like operation of the ten- 

 tacles. In Terehella conchilega the setiferous feet are only sixteen in num- 

 ber, the hooks and setae differing very slightly in model from those of the 

 former species (fig. 25). The feet effect a similarly ventral situation, and 

 the scale-like rugae under the thorax present a corresponding character, 

 only that in Terebella conchilega the ventral median line is painted red by a 

 ba7id of cutaneous pigment, which is commonly mistaken by cursory observers 

 for a large blood-vessel. In two other and nmch smaller species, which the 

 author has recently added to those generally known, the setiferous feet in one 

 are thirteen in number, and in the other eight ; in the latter they stand on 

 prominent peduncles, and differ strikingly from those of the other species. 

 The hooks vary only in the number of the teeth and in size (fig. 26). 



The tubeof the 7ere6eZ/«, according to the author's observation, is perforated, 

 not caecal, at its inferior termination. The fajculence rejected by the animal 

 is thus made to escape from the tube, by the force of a current of the external 

 water which is admitted into the tube, between the tube and the body of the 

 worm, and driven out through the posterior aperture of the tube by the sudden 

 retreating and swelling of the animal in its tube. It is accordingly found 

 that in the Terebellce there exists no provision, such as that which will after- 



