TEREBELLA. 193 



outwards, and from behind it, originate about fifty long, flexible, con- 

 tractile tentacula, much stronger than those of the preceding Terebella. 

 Three pair of branchiae, 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 branchiae 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 branchiae 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 scries 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, papillae, bristles, pencils, hairs, with other minutiae, 



2s 



