THE ORIGIN OF MAN 17 



was given to the group because of a false physio- 

 logical interpretation of the brachia or arms, for 

 the animals do not crawl on their arms as was 

 formerly supposed. The two more or less looped 

 or spirally rolled, fleshy, fringed arms, on the con- 

 trary, serve two functions: first, through move- 

 ments of the cirri and their cilia they attract cur- 

 rents of water into the shell, where the micro- 

 scopic food is extracted from it and fed into the 

 mouth; second, they serve for respiratory pur- 

 poses, that is, for the absorption of oxygen. All 

 Brachiopods are sexed, gregarious, marine ani- 

 mals, living from the strand-line down to the 

 great oceanic abyss, but their greatest abund- 

 ance is, however, in the shallow waters. 



The Mollusca or Shell-Fish comprises such 

 animals as clams, oysters, snails and the pearly 

 nautilus. They are soft-bodied animals, often in- 

 habiting shells to protect themselves. Most of 

 them are very sluggish and have unsegmented 

 bodies, and as they are devoid of limbs for crawl- 



