iS6 



ZOOLOGY 



in Arenicola, is even more conspicuous in some worms, e.g. 

 Chaetapte'rus ; but it is not a general feature of the group. 



Aphrodite, the sea-mouse, is a Polychaet of oval outline, 

 its notopodia bear a number of hairs, some iridescent, and 

 others which are matted together into a feltwork covering 

 the whole animal. This worm is further protected by a number 

 of plate-like elytra, also borne by the notopodia, but situated 

 beneath the feltwork ; they may be modified cirrhi, but the two 

 structures exist in some of the seg- 

 ments. Elytra are also found on 

 Polynoe. 



The nature of the tubes of the 

 Sedentaria is very various. It may 

 be soft, or of a parchment-like con- 

 sistency, and it may be strengthened 

 by a deposit of grains of sand or shell, 

 or it may consist entirely of the latter, 

 very skilfully agglutinated together. 



The Sabellidae (Fig. 99) and 

 Seepulidae, which live in fixed tubes 

 closed at the lower end, have a ventral 

 ciliated band, which is grooved in the 

 former family, whose function is to 

 carry up the undigested matter ex- 

 truded from the alimentary canal, and 

 pass it out of the tube. 



In both subdivisions of the Poly- 

 chaeta the pharynx is often protrusible ; 

 and in many Errantia it is armed 

 with stout teeth, which in some species 

 of Syllidae are said to be traversed 

 by the duct of a poison gland. 



In the Hesionidae (Fig. 100) and a few others a pair of 

 diverticula from the oesophagus, resembling in position the gland- 

 ular appendages of Arenicola, contain air, probably secreted 

 from the blood. The resemblance of these structures to lungs 

 has been noticed by many observers. Those families provided 

 with such structures have as a rule no branchiae. Another 

 family of worms, the Capitellidae, are provided with a 



Fig. 99. — Sabella vesiculosa, 

 Mont. After Montagu. 



