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 

 branchiae. 



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, shortening 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 XXVI. fig. 3, 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 



