1904.] NATURAL SCIENCES OF PHILADELPHIA. 685 



"The Reaction of Ants to Material Vibration," by Adele M. Fielde 

 and George H. Parker (September 20). 



The deaths of the following members were announced: Henry 

 Biinton Coxe, William S. Magee and Edward K. Tryon, Jr. 



The deaths of R. A. Philippi, and Edward von Martens, correspond- 

 ents, were also announced. 



Dr. H. a. Pilsbry made a communication on the stages of growth 

 and decline in the land mollusca. (No abstract.) 



Dr. J. P. Moore spoke of sexual polymorphism in annelids, with 

 special reference to the Polychseta. (No abstract.) 



October 18. 



The President, Samuel G. Dixon, M.D., in the Chair. 



Thirty-two persons present. 



Papers under the following titles were presented for publication: 



"The Orthoptera of Thomas County, Georgia, and Leon County, 

 Florida," by James A. G. Rehn and Morgan Hebard (October 11). 



"Annotated List of the Types of Invertebrate Cretaceous Fossils 

 in the Collection of the Academy of Natural Sciences of Philadelphia," 

 by Charles W. Johnson (October 14). 



Dr. Benjamin Sharp reported his experience during the summer on 

 a trawler from Hull which fished in the North Sea between England 

 and Helgoland, and on the cutter which brought the catch to London. 

 (No abstract.) 



A new Centrifuge. — Dr. Henry Emerson Wetherill described a 

 compact centrifuge that will do all the work of the ordinary centrifuge 

 with the advantages of being more compact, less complex, and more 

 easily cleaned. 



It does away completely with the heretofore unnecessary gearing 

 required for the revolutions, this being accomplished by a double 

 rotating motion produced by the twisting of rawhides or rope. This 

 to-and-fro motion gives a more level precipitation, and the magnifying 

 bulbous end of the graduated bottle enables a measurement of the 

 smallest amounts of precipitate. The bottles are tightly corked, thus 

 preventing the mixture of the precipitate with the supernatant liquid, 

 and serving as a safeguard in revolving infectious material. 



The instrument will fit in the vest pocket like a clinical thermometer, 

 and when one of the little pocket microscopes now to be had is used 



