156 ZOOLOGY 
in Arenicola, is even more conspicuous in some worms, @g. 
Chaetopterus ; 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 
SERPULIDAE, 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 ; 
Bea Savelin vacteolouat and in many Errantia it is armed 
Mont. After Montagu. | With stout teeth, which in some species 
of SYLLIDAE are said to be traversed 
by the duct of a poison gland. 
In the HestonrpaE (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 
