Ill 



dence is clear, how, in the course of ages, distinct tribes have 

 been formed, without supposing them to be a distinct creation." 

 "In the localities where the tribes overlap, the swarms will 

 appear in the given period of their natural lives." 



Dr. Burnett said, that from all that he had seen of the 

 Cicada septcndecim, seventeen years was the period re- 

 quired for its development, just as a certain number of 

 months was the period of the higher animals, and several 

 years that of some of the borers. In West Chester county, 

 he had seen it on rail fences surrounding a lot of land des- 

 titute of trees. The trees had been cut down, the ground 

 ploughed, and the rocks had been dug out four or five years 

 before ; yet on the seventeenth year the insect appeared. 

 In another place, the side of a house, which had been built 

 four or five years, was covered with the insects which had 

 emerged near it. The trees about it had been thinned out. 

 Dr. Burnett remarked, that there was some difference in 

 size and color in specimens from different localities. In 

 the different squares of Philadelphia are four or five dif- 

 ferent swarms which appear in different years. An old 

 man in Pennsylvania had told him that he had seen the 

 locust three times in his vicinity ; at each time after an in- 

 terval of seventeen years, and on or about the 21st of May. 



Mr. Girard said, he thought that slight atmospheric 

 causes might account for a difference of time in the appear- 

 ance of the insect at different places without supposing 

 them to have originated from different swarms. They 

 might all have come from a common stock. 



Dr. Theodore Cantor, of Calcutta, w^as elected a cor- 

 responding member. 



The skin of a South American serpent and several birds 

 were presented in the name of Dr. Cragin, of Surinam. 



