TEREBELLA. 195 
outwards, and from behind it, originate about fifty long, flexible, con- 
tractile tentacula, much stronger than those of the preceding Terebella. 
Three pair of branchizx, together forming a beautiful crest, four or five 
lines high, rise from the second and third segment, the former support- 
ing the first pair, and from their root the internal vessel extends visibly 
nine lines downwards. Each of these branchiz may be compared to a 
minute, luxuriant, florid specimen of coral, with spiral branches.—Plate 
XXVII. fig. 1. ; fig. 2, the same, enlarged.—Plate XXVIII. fig. 1, more 
highly magnified. 
But much embarrassment is experienced in determining the true 
configuration of so many living parts, and under such an arrangement 
in continual motion, expanding, contracting, and changing their form. 
According to the conventional comparison hitherto adopted, the mem- 
bers composing them seem to be four,—stem, bough, branch, and twig. 
Each bough originates by a short stalk from the common stem, and 
forks into two branches, while each branch forks into two twigs, or the 
whole extremities form screws and spirals. These extremities, probably 
amounting to 150 in all, exhibit a pleasing variety of line and figure by 
their incessant contraction and expansion. . The branchiz are remarkably 
tenacious of life. A detached section exhibited precisely the same action 
during eight days as when entire. This fact renders the source of their 
mechanical functions somewhat more perplexing than we should other- 
wise account it. 
Perhaps this species enjoys, to a certain extent, the reproductive 
faculties belonging to many of the vermicular tribes. A small fragment, 
preserving the whole series of tentacula, once occurred. Likewise a small 
specimen, which had been mutilated of all but a dozen, exhibited a 
fringe of the renovating organs under two lines long in a fortnight, and 
in five or six weeks they had become complete. 
Some naturalists have taken extreme trouble in endeavours to settle 
the number of parts, whereof the different regions, if I may call them so, 
of their bodies are composed. They have attempted to enumerate the 
number of rings, papillz, bristles, pencils, hairs, with other minutie, 
2B 
