208 REPORT— 1851. 



preserve the inferior end or bottom of their tube-house in a constant state 

 of tenantable purity and cleanliness, for the tube inhabited by the Amphi- 

 trite is caecal. Another provision, of a no less ingenious description, against 

 feeculent and noxious accumulation, is remarked in the organization of the 

 tail. At a given point the processes and branchiae abruptly terminate ; from 

 this point, the true tail, under the form of a cylindrical, contracted and coiled 

 portion, extends to some further distance, and then turns upwards parallel 

 with the body of the worm, in order with the greater mechanical advantage 

 to project in the direction of the upper orifice of the tube the faical refuse. 

 This sagacious contrivance has not eluded the discriminating eye of Cuvier. 



In A. auricoma (fig. 28) the papillee and cirri of the feet are entirely 

 absent ; tiie hooks, however, similarly disposed on transverse eminences, are 

 stronger and larger, and the setse are serrated only on one side. The tail- 

 like appendage to the inferior extremity of the body, in all respects but one, 

 is formed on the model of that of the former species. One labium of the 

 terminal orifice is here extended into a flap-like process, which by a sudden 

 act of muscular contraction, imparts a smart blow to the fceculent mass as it 

 escapes from the intestine, and thus effectively conveys it to the upper out- 

 let of the tube. This terminal extreme of the alimentary canal is richly 

 provided with large and vigorous cilia. In Sabina Poppcea (Williams) the 

 anal orifice is fringed with fleshy processes, which, clothed with vibratile 

 cilia, fulfil offices which in the former species devolved on a specially formed 

 tail. In all cases the office of the hooks is the same. 



It is here in alliance with the Amphitrite that the author would locate the 

 little rock-boring Leucodore ciliatus. Its occipital tentacles are only two in 

 number — long, muscular and mobile ; they are subservient to prehension. 

 The thoracic region of the body is definitively marked from the abdominal, 

 and is terminated by a foot much larger than any of the rest. The rows of 

 hooks (fig. 29, «) are placed dorsally ; each hook is double-toothed and 

 supported on a long stem. The branchiae are dorsal like those of Amphitrite 

 alveolata. The feet are biramous, carrying a double bunch of setas 

 (fig. 29, h). These latter occur under three varieties of form ; some are 

 awl-like for piercing ; some are pincer-like for grasping ; others are plain- 

 edged for scraping. Nothing in the structure of this little worm equals 'the 

 tail' in beauty and singularity. The lower extremity of the tube inhabited 

 by it is caecal and smooth, and not drawn out, as in other cases, into Zifine 

 conical cell. The tail is organized peculiarly and with express reference to 

 this formation of the bottom of the cell. It is expanded with geometrical 

 exactitude into a hollow cone, the anus occupying its receding apex. This 

 remarkable and most beautiful apparatus acts on the principle of the sucher. 

 Its sides are composed of a membranous muscle. When it is being applied 

 to its point of attachment, the worm lets down its weight upon the part, in 

 order to press out the water with which the bottom of the tube may be 

 filled. The tail is then suddenly drawn up, a movement by which the 

 apex of the cone is raised from the surface of contact. The pressure of the 

 ■water with which the tube is filled is now rendered operative, and the little 

 worm amid the raging billows is securely anchored to its cell. It is impos- 

 sible to discover in this wondrous vital mechanism a single particular in 

 which the principles of hydrostatic pressure are not minutely obeyed. 



In the organization of the feet of the familiar genus Arenicola, there 

 is little to call for remark. Formed to move readily through loose sand, 

 pedal appendages are scarcely required. The brushes of bright iridescent 

 setae (fig. 30), which arise on either side out of the twenty anterior rings of 

 the body, constitute the sole motor elements of the appendages. The thir- 



