ANARTHROPODA. 125 



part of the alimentarj canal is muscular, and can be turned 

 inside out, or protruded beyond the true opening of the 

 mouth. The pseudo-haemal system is well developed, and its 

 contained fluid is mostly red. Respiration is effected by ex- 

 ternal processes, gills, or branchiae, arranged in tufts placed 

 along the sides or back of the body, and not confined to the 

 immediate neighborhood of the head, as in the Tubicola. The 

 sexes are in difiorent individuals, and the young pass through 

 a metamorphosis. 



Among 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. 



