ON THE BRITISH ANNELIDA. 211 



forwards by the anterior. Each ring throughout the bodj' has its own legs, 

 which move with perfect independence. Remarkably long and gracefully 

 slender, then, as the body of this worm may be, every part advances or recedes 

 at one and the same time, and locomotion is active and vigorous. Under 

 such a complicated repetition of oars, hooks, paddles and fins, a final result, 

 unerringly harmonious, is obtained, which man's ingenious handivvork would 

 attempt in vain to imitate. 



The Nereids constitute the most common and most obtrusive family of 

 sea-side Annelids. The majority of the species inhabit galleries, detectable 

 under every stone between tide-marks, along which they crawl like subter- 

 ranean beasts of prey. They are by no means inviting to the eye, either by 

 their colour or conformation. They are carnivorous in habits, and perpe- 

 tually on the watch for prey. In nearly all species the feet are constructed 

 with express reference to progression on solid surfaces. Among the Nereids, 

 in the classification of species, it is very important in determining the cha- 

 racters of the feet, that those compared in difi'erent individuals should be 

 selected as nearly as possible from the same region of the body. The ce- 

 phalic feet in one should be compared with those in another species from the 

 same division of the body ; those from mid-body with others from mid-body, 

 and those near the tail with others from the same part. If this be not done, 

 and done with exact and minute accuracy, it will be found quite impossible 

 to arrive at a clear knowledge of constant and invariable anatomical cha- 

 racters for the definition and limitation of species. In all Nereids the feet 

 are biramous, but coalescent at the base. Every foot, in every species, 

 consists of a superior and an inferior cirrus, three papillae, generally de- 

 scribed as branchial, and two tubercles armed with compound bristles. 

 The superior tubercles are always situated between the dorsal and second 

 papillae, and the inferior tubercle between this and the ventral papillae. In 

 Nereis margaritacea the setae are jointed, the articulated piece being serru- 

 lated, and seeming calculated only for walking. The setae of the superior 

 feet always, in the Nereids, differ in structure from those of the inferior feet. 

 In N. margaritacea the extreme portion is sabre-shaped and fine-edged 

 (fig. 35). In N. renalis the same portion presents a finely toothed edge 

 (fig. 36). In the superior foot the setae are strong, and the connected piece 

 is short, strong, curved, and always serrated ; while those of the inferior are 

 more slender, and longer, the connected piece being needle-shaped and pro- 

 longed. These worms are endowed with no mechanical means for the con- 

 struction of their galleries, unless they be those of the jaws and proboscis. 

 The feet are mainly constituted for walking ; the setae, if destined for such 

 work at all, can only scrape and polish the interior of the gallery when made. 

 Viewed by the light of mechanical principles, nothing can be so obvious as 

 the reason why the setae in these as in nearly all other Annelida are jointed. 

 If they consisted of rigid, unbending levers, it is manifest that they would 

 prove most awkward additions to the sides of the animals ; if fixed too deeply 

 in the surrounding soil, they would not act at all as levers ; if too super- 

 ficially, the worm would be compressed in its tube at the moment when the 

 setffi of the opposite feet would meet in a straight line. These difficulties are 

 effectually and skilfully obviated by the introduction of a joint or a point of 

 motion on each seta. This is one instance among many, which the eye of 

 the mechanician would detect in the organization of the Annelida, in which 

 nature takes adroit advantage of mechanical principles in the attainment of 

 her ends. 



The Phyllodocidce are by common consent the most ornamental worms 

 among the Nereidce (" Virgines pulcherriraae inter Nereides," Fab.). They 



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