OF ARTS AND SCIENCES. 441 



Professor Peirce made a communication upon the grounds 

 of the probability of intermercurial planets, and upon polar 

 forces. 



Professor Agassiz gave an account of his recent investi- 

 gations of the structure of the Radiata, and discussed their 

 general homologies in reference to the natural limits of that 

 branch of the animal kingdom. He proceeded to a compari- 

 son of their special homologies, and concluded that the Radi- 

 ata embrace only three distinct classes, the Polyps, the Aca- 

 lephs, and the Echinoderms ; that the Hydroids are genuine 

 Acalephs, as well as the Ctenophoras, and that the Siphuncu- 

 loids must be excluded from the type of Radiata. 



An oral communication was received from a delegation 

 from a committee of citizens engaged in promoting the con- 

 templated expedition of Dr. Hayes to the Arctic regions, and 

 the influence and good offices of the individual members of 

 the Academy were solicited in its favor. 



VOI-. IV. 56 



