ANNELIDA 



along the entire length of the 

 Dorsibranchiate order, are here 

 transferred to the head, where they 

 form long and delicate instruments 

 of iouch, and, most probably, assist 

 materially in distinguishing and 

 seizing prey ; the branchiae, like- 

 wise, are no longer met with upon 

 the segments enclosed within the 

 tegumentary tube, but are placed 

 only in the immediate vicinity of the 

 head, where they form fan-like ex- 

 pansions, or ramified tufts, so ar- 

 ranged as to be most freely exposed 

 to the surrounding medium. The 

 mouth placed at the origin of the 

 tentacular cirri is a simple orifice 

 closed with a valve-like flap or up- 

 per lip, but is unprovided with any 

 dental structure. The alimentary 

 canal is generally a simple and 

 somewhat capacious tube which tra- 

 verses the axis of the body ; but in 

 some species, as in Sabella pavo- 

 nina, it assumes a spiral course, 

 making close turns upon itself from 

 the mouth to the anal aperture, 

 which is always terminal. The cir- 

 culating system probably resembles, 

 in its general arrangement, that 

 of the Dorsibranchiate worms, the 

 course of the vessels being modified 

 in accordance with the altered posi- 

 tion of the branchiae ; but of this 

 we have no certain knowledge, nei- 

 ther are we acquainted with the na- 

 ture of the generative apparatus, 

 and the scattered remarks of au- 

 thors upon this subject are to the 

 last degree vague and unsatisfac- 

 tory. 



Fig. .97. 



