TEREBELLA. 185 
but instant cessation, followed by speedy disfiguration and decay, are con- 
comitant on death, rendering every attempt to ascertain their structure 
fruitless. 
This may be well understood from the presence of a serpentine in- 
ternal vessel appearing blue, which, winding through most of the body. 
seems to discharge much of its contents during vigorous life into the 
branchie. 
The first or highest pair of these organs is the largest, and all of an 
arborescent form. Each, as viewed individually, consists of a main trunk, 
with boughs and branches, shortenimg as they rise towards the summit 
of their principal parts respectively. The boughs, in alternate arrange- 
ment, diverge from the trunk ; the branches, single, in pairs, or in triplets, 
are arrayed around the boughs. Most of the subordinate parts originate 
from the convexities of those sustaining them.—Plate X XVI. fig. 5, en- 
larged. A section of one of the extremities exhibited thirteen promi- 
nent cups under the microscope, fig. 4. ; none could be discovered on 
another. The beautiful red of the branches fades, and is converted into 
a green, as the animal weakens ; and then, as when in a dying state, the 
whole body tends to the same colour. 
Under the microscope, a convoluted intestinal organ was exposed in 
a young specimen, not half an inch long ; likewise were discovered by 
the same means, numerous round, black specks, like so many ocelli, un- 
der the margin of the frill. 
It is not improbable that certain organization, resembling tubercles 
or prominences, evidently distinct from the neighbouring parts, may be 
of a glandular nature. We cannot ascertain the various secretions from 
the body of the lower animals, nor the precise organs instrumental in 
producing them. 
But the use of some of the rest of the external organs of this ani- 
mal is easily seen, for example, the tentacula, and it proves most amus- 
ing to the observer. 
If a specimen be dislodged from its tube, it swims by violent contor- 
tions in the water, after the fashion of the Nereis, and some other worms 
2A 
