TEREBELLA. 189 
time, a confused assemblage of tubular projections and orifices are con- 
nected with the main structure. 
A tube, constructed with considerable regularity on the side of a 
spacious vessel, where the animal has partly saved its labour, is represent- 
ed on Plate XXVI. fig. 5. 
Sometimes while the anterior part of the Terebella occupies its tube, 
the posterior extremity is suddenly reversed, to discharge a quantity of 
sand from the same orifice, and as suddenly withdrawn. This is accom- 
plished by the body folding within the tube, and the purpose of reversal 
may be to discharge the materials within reach of the tentacula. Thus 
there must be an internal reservoir. This part, however, very seldom 
comes under observation. I believe the whole animals of the genus can 
reverse themselves in the tube, so as to carry on the operations from 
either end. 
In the natural state, a singular kind of tuft terminates, on indeed 
both extremities of the tube, proving an excellent guide to the animal's 
retreat. But such tufts are rarely formed in confinement. If they do 
appear, it is generally in May or June. The tuft consists of thirty or 
forty threads of sand, nearly nine lines long, fashioned by agglutination 
of many grains of sand, laterally or longitudinally together. In the 
course of a night a young specimen fabricated two threads, each being a 
single row of about thirty grains, at the opposite sides of the orifice. If 
the tube rises amidst the heterogeneous mass of matter on the shore, the 
threads issue from the edge of the orifice, many of them forking about the 
middle into two or more lines of sand. The use of these tufts is uncer- 
tain, whether as a defence against enemies, as a nidus to receive the 
spawn, which, I have never had the fortune to see, or to entangle prey, 
which is less probable. Frequently both tufts are forsaken in their ori- 
ginal position by the subsequent prolongation of the edifice beyond 
them. 
The Terebella is a very lively, active animal, but of great timidity. 
Its energies seem to be aroused chiefly by the state of its dwelling, to- 
wards the enlargement of which incessant labour is devoted. By sunder- 
ing a long tube below, while the architect is above, the observer will 
