324 



POLYCHAETA 



distinguishable, which may be denoted by the letters A, B, and 

 C. The most anterior region, A, is flattened, and carries 

 nine pairs of conical lobes with delicate chaetae, though the 

 fourth lobe possesses special stouter chaetae (as in Polydora). 

 The anterior end of the body terminates in a wide funnel, the 

 boundary of which is formed chiefly by the peristomium ; on il 

 dorsal surface is a pair of tentacle-like processes (peristomial 

 cirri) ; the region between which represents the prostomium. 



The second region, B, is very curiously modified ; it is formed 

 of five segments. The most anterior is produced on either side 

 into a great wing-like process, which in life is directed forwards 

 above the region A. Each is grooved on its inner side, the 

 ciliated grooves being continuous with a median groove running 

 forwards along the back of A ; this apparatus serves to bring 



food to the great funnel -like mouth. 

 The next segment (twelfth) carries a 

 dorsal and ventral " sucker," representing 

 the parapodia. Each of the segments 13, 

 14, 15 carries a membranous fold en- 

 circling the body. By the constant 

 movement of these " fans," which have 

 nearly the same diameter as the tube, 

 a current of water is constantly washed 

 over the animal. The fans represent 

 the notopodia; the neuropodia are bilobed 

 rounded knobs. The region C consists 

 in the adult of about thirty segments, 

 all alike, and less modified than the pre- 

 ceding. The animal is the most truly 

 tubicolous of the Polychaetes, and is 

 much modified on this account. No 



Fig. 173. Chaetopterus. (From 



Panceri.) Natural size of a locomotor chaetae are present, though 

 young specimen. A is the ^e or rea t wings and notopodial processes 



anterior region of the body ; , * t x . 



of region C contains chitinous bristles, 



not project ; l the 



B, the middle region ; C, the 



hinder region c, Peristomial j^ however, do 



cirri ; a, sucker ; e, the ' ' 



great "wings";/, the first of anterior region with its stiff chaetae, and 



the three fans" ; m, mouth. ^ neuropodial uncina l pl ateS of the rest 



of the body serve in its movements up and down the tube, while 

 the " suckers " fix the worm temporarily to the wall of its house. 



1 Compare Stemaspis, p. 336. 



