184 TEREBELLA. 



The littoral Terebella, expelled from its tube, is of a vermicular form ; 

 the body seven or eight inches long, and a quarter of an inch thick towards 

 the head, and consists of numerous segments tapering towards the posterior 

 extremity, which terminates in several points. Plate XXVI. fig. 1. Six- 

 teen retractile pencils, each of fifteen or twenty bristles, border the sides 

 of the upper segments, which farther down degenerate to stumps. The an- 

 terior part of the body consists of a thin frill, divided into three portions, 

 surrounding the roots of sixty, seventy, or a hundred tentacula, according 

 to the age or dimensions of the specimen, with the mouth like a scoop 

 in the midst of them. Immediately behind this frill, three pair of the 

 most beautiful scarlet branchiae rise half an inch high. The animal is 

 universally of peach- blossom colour, variable in a redder or browner tinge, 

 with a broad, taper, smooth, velvet, bright carmine stripe, descending 

 along the belly between a transverse row of ellipses. Plate XXVI. fig. 1, 

 Terebella, reduced ; fig. 2, section of the body. 



An easier guide than following the preceding description, consists 

 in simply observing the formation of the branchiEe, to identify the 

 different species of the Terebella. These organs are extremely diversi- 

 fied, sometimes in number, always in structure. It is somewhat singu- 

 lar to remark, that naturalists give one set of branchiae as that of the 

 Terebella conchilega, though actually not belonging to the species, for 

 an illustration of all the rest. But we must allow that the observer's 

 most attentive inspection is indispensable. This organ becomes a micro- 

 scopical object, about which no one can readily satisfy himself; its 

 expansion and contraction are incessant, thence nothing is of more diffi- 

 cult delineation. 



The branchias of every species of Terebella, I say, are different. 

 Here they are so complex and luxuriant, they abound in such numerous 

 points, extremities, and curvature ; their shades and intensity of colour, 

 and the alternation of shape are so variable, that no object is more 

 beautiful and interesting to behold, or more difficult to be rendered in- 

 telligible by description. To attempt it would be vain. The mind alone 

 must conceive it. During life, the motion, the enlargement, reduction, 

 and spiral twisting of the branchite, singly or collectively, is perpetual, 



