ANARTHROPODA. £35 
of the alimentary canal is muscular, and can be turned inside 
out, or protruded beyond the true opening of the mouth. The 
pseudo-hzmal system is well developed, and its contained fluid 
is mostly red. Respiration is effected by external processes, 
gills or branchiz, arranged in tufts placed along the sides or 
back of the body, and not confined to the immediate neighbour- 
hood of the head, asin the Zzdzcola. The sexes are in different 
individuals, and the young pass through a metamorphosis. 
Amongst the best known and commonest of the Errant Anne- 
lides are the common lob-worm (Arenicola piscatorum) of our 
coasts, which is constantly used by fishermen for bait ; and the 
sea-mice (Aphrodite and Polynoe), some of which attain a large 
size, and are conspicuous for their iridescent bristles. Other 
less abundant forms may be readily obtained by searching under 
stones at low water. 
