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Transactions of the Society. 
beauty and gracefulness of which render it an interesting question 
how the animal manages to construct them ; and the method actually 
adopted, which I observed last year, has, I believe, not been pre- 
viously described. 1 n order to render a clear account of the process, 
it is necessary to preface a few words descriptive of the animal. 
These worms, which are to be found on almost all the sandy sea- 
shores of Europe, vary in size from an inch to possibly eight or nine 
inches in length, according to age. The body is divisible into two 
main portions — the anterior, which in a large specimen is a quarter 
of an inch or more in width, consisting of about twenty segments ; 
and the posterior, which is prolonged into a cylindrical tail, of small 
diameter, composed of numerous segments. The anterior extremity is 
the prostomium, from the back of which spring a large number of 
long, simple, filamentous tentacles almost surrounding the mouth. 
The buccal segment, which follows, is produced in front and forms an 
under lip. Then come three segments, each bearing a pair of beau- 
tiful arborescent red branchiae, followed by the notopodial fascicles, 
containing their peculiar setae. Ventral to these are situate the oval 
tori, bearing the uncini, which latter are continued throughout the 
body, the form of the tori varying in the posterior portion of the 
animal. The tentacles, the prostomium, and probably the lower lip, 
are the organs employed in the building operations. The tentacles, 
which in section present a cordate shape (fig. 8), are long, hollow, 
tubular, very extensile filaments, communicating with the body-cavity, 
the perivisceral fluid from which travels freely up them, favouring 
their extension and contraction. These filaments are richly provided 
with vibratile cilia on the two edges, and also on the central line of 
the side which is turned towards the mouth of the worm. Their sides 
are covered with mucus-secreting cells, and the two outer edges of 
the tentacles are capable of being folded together longitudinally, so 
as to form either a hollow cylinder or a semicylindrical channel 
at will. 
This power, assisted by the secreted mucus, enables them to grasp 
at any point small stones or grains of sand, which are then passed 
forward to the prostomium, either by ciliary, or a kind of peristaltic 
action (the sides of the tentacle closing up behind the stones), or by 
sudden muscular contraction of the tentacle, or by a combination of 
all three. The chief office of the tentacles, in the building work, is 
to collect and carry materials, though they also sometimes tem- 
porarily support large stones, shells, &c., which are being fastened to 
the edge of the tube. They also collect food for the worm, and are 
believed to discharge certain other functions, the discussion of which 
is outside the object of this paper. The large upper lip is a most 
wonderful organ, capable of assuming an infinite variety of forms, 
and is, if I may use the expression, the bricklayer. 
In what may be called common walling, i. e. building the tube 
itself, the operation is simple, and easy to observe. Sand-grains, 
