Animals Before Man 



A brachiopod, showing the curious spiral 

 loop. 



pion has been found, showing very clearly the 

 existence of life on land. The mollusk-like 



brachiopods not 

 only multiplied 

 in numbers dur- 

 ing the Ordo- 

 vician, but in- 

 creased in com- 

 plexity by developing curious loops and spiral 

 structures inside their shells as well as a better 

 form of hinge- joint. 



Trilobites have increased in numbers, kinds, 

 and size, reaching at this time the highest point 

 in their history. Perhaps the most notable ad- 

 vance is that made by true mollusks of the 

 class Cephalopoda * in the development of 

 forms related to the pearly nautilus, a shell 

 that unfortunately does not sail the unruffled 

 main, but creeps humbly along the bottom of 

 the sea. The nautilus is a relative of the 

 naked squids and cuttlefishes, but, unlike them, 

 dwells in a closely coiled shell of many divi- 



* Head-footed, a name given on account of the tentacles ar- 

 ranged about the head, although, oddly enough, these are univer- 

 sally called arms, 



72 



