76 



Order VI. ANNELIDES. 



Chetopodes ( — ), Blainv. Princip. d'Anat. Comp. i. tab. /• sp. 177. 

 Annelides, De Quatrefages in Ann. des Sc. nat. viii. 99 (1847). 

 Annulata appendiculata polychaeta, Grube,Fam. Annel.26. 



Char. Worms segmented, the segments forming a section of a 

 cylinder or semicylinder, and furnished on each side with prominent 

 lobular or wart-like feet armed with many retractile bristles of 

 various kinds, in one, two, or three fascicles : head either distinct 

 Avith organs of sense, or indistinctly defined with tentacular filaments 

 on its crown or sides : branchiae variously attached, usually combined 

 with the feet, filamentary, foliaceous, or arbuscular, rarely obsolete 

 or cutaneous : anus opposite to the mouth, terminal, and usually pro- 

 tected with styles or lobules. Blood red or green, circulating in close 

 vessels : respiration aquatic : zoophagous or geodephagous : the sexes 

 separate or united in the same individual : marine or littoral. 



It may be useful to give a brief explanation of the nomenclature 

 employed. 



The Body is the entire worm. The form is defined by familiar 

 words, in general used in their common acceptation, but it is con- 

 venient to call it lumhriciform, when it is nearly cylindrical, like the 

 Earth-worm ; scolopendriform, when it is flattened on both dorsal and 

 ventral surfaces with nearly parallel sides, like the Centipede ; and eru- 

 ciform, when it is thickish in proportion to its length, antl grub-like. 



The body is formed of a specific number of Segments developed 

 in longitudinal succession, and divided from each other by a plain 

 suture. They are annular ; and subdivided sometimes into rings by 

 circular folds of the skin. 



The Segments are similar when they resemble each other in 

 structure generally ; and they are dissimilar when some vary from 

 the others in any addition, or abstraction of organs. 



The Segments are of three kinds more or less distinctly marked, 

 — the cephalic, — the thoracic, — and the abdominal. 



The Cephalic is that portion of the body anterior to the first 

 transverse suture. It may be composed of three or more segments 

 in a more or less intimate union, but the demonstration, however 

 useful in theoretical, is useless in descriptive anatomy. 



When the aspect of the cephalic portion is such that we cannot 

 call it otherwise than a head, the worm is said to be cephalous 

 (No. IV. fig. 8) ; when it differs little from the other segments behind, 

 and appears almost a continuation of them, it is svbcej)haloiis (figs. 

 9, 11); and when there is no appearance of a head, and the front 

 terminates abruptly, the worm is acephalous (fig. 10). 



