390 PROCEEDINGS OP THE ACADEMY OP [1885. 



powerful armor and teeth. The toothless invertebrates probably 

 still fed on small, unarmored prey. 



In all cases, however, the most powerful animals would have 

 little or no need of defensive armor. The armed Ganoids prob- 

 ably needed defense against each other. But it is likely that 

 they were mainly defended against the great Elasmobranchs, 

 which were the ruling tyrants of the seas, and which needed no 

 defense beyond their osseous tubercles and spines, this type of 

 armor permitting the utmost flexibility of motion. As Packard 

 says of them : "Sharks and skates are engines of destruction, 

 having been, since their early appearance in the upper Silurian 

 age, the terror of the seas. Their entire structure is such as to 

 enable them to seize, crush, tear and rapidly digest large inverte- 

 brates, and the larger marine members of their own class. Hence 

 their own forms are gigantic, soft, not protected by scales or 

 armor, as they have in the adult form few enemies." Such seems 

 to have been the outcome of the agencies of attack and defense in 

 the pakeozoic era, a minor series of soft-bodied animals, an inter- 

 mediate series of strongly armored animals, and a superior series 

 of animals, adapted to break through the strongest defensive 

 armor. 



As a result of this evolutionary process the powers of assault 

 and defense again became equalized, and armor lost its special 

 value as a defensive agent. From that time forward defense 

 seems to have adopted a new expedient, and a fresh series of modi- 

 fications arose. W armor had become of li.ttle value in defense, 

 flight remained useful. But armor impeded flight, both from its 

 weight and the rigidity of body it produced. Thus for the 

 development of speed, agility and flexibility of motion, it was 

 necessary to get rid of armor ; and during the whole of the later 

 geological periods this has been the character of the evolutionary 

 process, at least in the free-moving animals. Food animals have 

 thrown off their armor, and trusted to speed and flexibility of 

 motion for safety. Carnivorous animals have followed in the 

 -Mine direction, and got rid of their disabling armor. 



If we puisne this subject further we can perceive the succes- 

 sive adoption of several other expedients. It is impossible to 

 say whether flight or pursuit first aided in the development of 

 winged animals. Bui it is evident that Hying food animals would 

 lie nearly safe from the attacks of surface carnivora, and would 



