Amphineura 25 



turn to a chosen resting place after each feeding excursion. Their 

 sizes range between five and one hundred fifty millimeters. 



The sexes are separate. Some species lay their eggs singly or 

 in unattached strings, some others retain the ova within the mantle 

 cavity until the shell is formed. 



In some tropical countries the muscular foot of large chitons 

 is used as food. Natives of some of the West Indian islands call it 

 "sea beef", and either eat it uncooked or make of it the chief ingre- 

 dient in a savory loblolly. In the far north, chitons are a reputed 

 cure of seasickness but only when swallowed alive. 



The remarkable ellipsoidal shell of the chitons covers only the 

 dorsum of the animal. It is multivalvular, consisting of eight thin 

 plates or valves, transversely wide, gently arched from side to side, 

 and longitudinally keeled in the midline. Each valve articulates with 

 the valve next behind it with a slight overlap toward the posterior 

 end. All the valves are held together and in relation to each other 

 by a girdle of tough, leathery tissue which surrounds the entire peri- 

 phery of the articulated valves. The overlap of the valves facilitates 

 bending — and the chiton's defensive attitude is assumed by ap- 

 proximating end to end for protection of the vulnerable body. Just 

 so in the early Dark Ages armor plates were fastened to leather, 

 often by rivets; the leather foundation gave flexibility to the coat of 

 mail. 



When the valves are separated, which is easily done by a short 

 soaking in fresh water, the head and tail plates are seen to diflFer 

 from the six intermediates. The anterior valve is roughly semi- 

 circular with a median elevated apex. The posterior valve is much like 

 the intermediates but slopes abruptly to a rounded margin. The 

 intermediate valves are rectangular in outline and show three 

 more or less well-defined areas upon their outer surface; along the 

 keeled mid-ridge of the shell is the jugal or dorsal tract, on each side 

 are the pleural tracts, which in some genera are demarcated from 

 the lateral tracts by an oblique line from near the center of the post- 

 erior valve margin toward the outer end of the anterior margin; the 

 sculpture of these areas is important in diagnosis. The valves of most 

 chitons have projecting plates at the free edges which are covered 

 by, and serve as attachment for, the girdle. 



