ANNELIDA : — TEREBELLA. 



627 



of grains of Sand, fragments 

 of Shell, &c. ; whilst they are 

 distributed along the two 

 sides of the Body in such as 

 swim freely through the 

 water, or crawl over the sur- 

 faces of rocks, as is the case 

 with the Nereidce, or simply 

 bury themselves in the sand, 

 as the Arenicola or 'Lob- 

 Worm. ' In these Respiratory 

 appendages the Circulation of 

 the fluids may be distinctly 

 seen by Microscopic examina- 

 tion ; and these fluids are of 

 two kinds, — first, a colour- 

 less fluid, containing numerous 

 cell-like corpuscles, which can 

 be seen in the smaller and 

 more transparent species to 

 occupy the space that inter- 

 venes between the outer sur- 

 face of the Alimentary canal 

 and the inner wall of the 

 Body, and to pass from 

 this into Canals which often 

 ramify extensively in the 

 Respiratory organs, but are 

 never furnished with a re- 

 turning series of passages, — 

 and second, a fluid which is 

 usually red, contains few 

 floating particles, and is en- 

 closed in a system of proper 

 vessels that communicates 

 with a central propelling 

 organ, and not only carries 

 the fluid away from this, but 

 also brings it back again. 

 In' Terebella we find a dis- 

 tinct provision for the aera- 

 tion of both fluids ; for the 

 first is transmitted to the 

 tendril-like Tentacula which 

 surround the mouth (Fig. 

 327, 6, 6), whilst the second 

 circulates through the beau- 

 tiful arborescent Branchiae 



Fig. 327. 



Circulating Apparatus of Terebella 

 conchilega : — a, Labial ring ; 6, b, Tenta- 

 cula ; c, first segment of the trunk ; 

 d, skin of the back ; e, Pharynx ; /, In- 

 testine ; g, longitudinal muscles of the 

 inferior surface of the body; h, Glan- 

 dular organ (liver ?) ; i, organs of Gene- 

 ration ; j, Feet ; k, k, Branchiae ; I, Dorsal 

 Vessel acting as a Respiratory Heart ; 

 m, Dorso-Intestinal vessel ; n, Venous 

 Sinus surrounding oesophagus ; n', in- 

 ferior Intestinal vessel ; o, o, Ventral 

 truak ; p, Lateral Vascular branches. 

 s s 2 



