ON THE BRITISH ANNELIDA. 215 



four strong teeth are affixed, which perform the business of so many pickaxes, 

 in tearing and disintegrating the soil. This worm possesses no other instru- 

 ment for pioneering its way through the ground than the proboscis ; though 

 a part of the alimentary system, it has therefore been cursorily mentioned 

 here. The antennae, which exist in Glycera under the character of four 

 minute horns, crowning prettily the apex of the conical head, are exclusively 

 organs of touch. The feet are prominent, and supported on a long muscular 

 uniramous base. They are separated from each other by an appreciable 

 interval. The branchia, as already described, is dorsalmost. At the in- 

 ferior base of this appendage is situated the setiferous process of the dorsal 

 foot. The setae are very protrusile and jointed ; the articulated portion 

 being long and extremely finely pointed and penknife-shaped. In the centre 

 of the setae is observed a strong rigid spine, which, in all the Annelids in which 

 it exists, contributes materially to the mechanical strength of the foot (fig. 41). 

 Below the setiferous process is found a conical cirrus of a length equaling the 

 setae in their retracted position. This organ can be of little service in 

 swimming ; it is exclusively tactile. The inferior foot is an exact repetition 

 of the superior, wanting the branchial process, while the cirrus is larger and 

 flatter than the corresponding part of the dorsal. Two strong round taper- 

 ing styles are superadded to the tail, which materially assist the worm in 

 its progress through its native soil. Actual observation of its habits can 

 scarcely be required to convince the intelligent naturalist that Glycera is 

 almost entirely incapable even of sustaining itself in water. In this element 

 its movements are those of irregular contortions and oscillations from side to 

 side, convulsive struggles without progress. The study of its structure suf- 

 fices in proof of the inference that it was made for the exact place in 

 nature in which it is found. If the soil is too hard, its struggles to move are 

 fruitless ; if too dry, it is paralysed ; if too wet, the proboscis is rendered use- 

 less, and it shows immediate evidence of discomfort. Its organization fits it 

 only for a soil of peculiar consistence and structure ; and such exactly are 

 the circumstances under which it is found. The above considerations have 

 arisen out of those bearing on the mechanism of the appendages in this 

 merry and beautiful little worm. 



Like Glycera, Nephthys is a frequenter of the sandy shore ; it selects 

 spots, however, in which the soil is quite different in several respects from 

 that ol' the native places of Glycera. Nephthys lives in fine sand saturated 

 with water. It advances through such a medium with a swimming motion. 

 It is admirably organized for progression in water. The cirri of its feet 

 consist of large fan-shaped processes, the plane of which is vertical and suitably 

 appointed for swimming. The setae are composed of two distinct layers, of 

 which one is placed anterior and the other on the posterior surface of the 

 cirral lamina (fig. 42). The brush of setae on both sides radiates from a 

 common centre at the root of the foot. The posterior setae are constructed 

 on the exact pattern of the flattened fibre of striped muscle, ending in a fine 

 point ; they are strong and elastic. Those anterior to the cirrus are much 

 longer than the former, and assume the shape of sharp-pointed, finely serrated, 

 bi-edged blades. From the inferior base of the superior foot the branchia 

 depends ; from the same point of the inferior, a conical cirrus. The ventral 

 foot in all other characters is a precise repetition of the dorsal. 



Nephthys is distinguishable from all other Annelids by its remarkable 

 tail. It is a median style, extending to a considerable distance backwards, 

 like the occipital ornament in the head-dress of the Chinese. It is singularly 

 flexible and mobile. Its use can scarcely be conceived, unless it be that of 

 defence for the posterior part of the body of the worm. In swimming, how- 



