198 TEREBELLA. 
The body extends about five inches ; and it is provided with about 
seventy long and strong tentacula, stretching nine inches, which are 
capable of sweeping an area eighteen in diameter around the head, while 
the body remains stationary. 
Six branchiz are disposed in three pairs, the highest pair the longest, 
the other two successively decreasing. These are fine and florid organs, 
of peculiar formation, appearing somewhat mottled like birch bark un- 
der the. microscope. These parts are alike numerous as those of the 
others, but they do not abound in similar curvatures, their extremities 
terminate in forks like thorns. Their action is incessant, whence, toge- 
ther with the slightest movement of the animal withdrawing them every 
instant from the field of the microscope, excessive difficulty obstructs 
the delineation of even a small portion magnified, Plate XXVI. fig. 8. 
Thirteen transverse furrows indent the upper portion of the body, which 
is subdivided into numerous annulations, and tapering down towards the 
lower extremity. 
As the animal extends its body, the annulations of the upper por- 
tion are quite obliterated. 
The whole is of a fine reddish-brown colour, the surface universally 
speckled with low white tubercles, rendering it altogether a very beauti- 
ful object. 
This Terebella constructs a wide loose case of fine sand, so large 
that it can reverse itself within, and sometimes the tentacula are seen 
protruding from both orifices. At first, from its general resemblance to 
the figulus, I thought it might construct a tube of mud or clay. But it 
testified no disposition to work in either, though employing some frag- 
ments of comminuted shell along with the sand. Night is the season of 
its greatest activity. 
When dislodged from the tube for the purpose of inspection or de- 
lineation, and then supplied with sand, the higher portion of the body 
is that which is first protected by the rudiments of a new edifice. 
The specimen represented Plate XXIX. fig. 1, having been com- 
mitted to a wide vessel with a quantity of sand, it continued lurking 
within at its work. Desirous of observing its future operations, I then 
