1879.] NATURAL SCIENCES OF PHILADELPHIA. 203 



Sept. 23. 

 The President, Dr. Ruschenberger, in the chair, 

 Thirty-five persons present. 



Sept. 30. 



The President, Dr. Ruschenberger, in the chair. 



Thirtj'-two persons present. 



The death of Edward Peace, M.D., a member, was announced. 



On Grifitatella Mae. Prof. Leidy remarked that a few days ago, 

 while rambling in the Park with his little daughter, she had called 

 his attention to what she supposed to be numerous caterpillars at 

 the bottom of a brook. On examination they proved to be an ex- 

 traordinary accumulation of Cristatella Mae. This species of poly- 

 zoon, or fresh-water ciliated polyp, he had discovered at Newport, 

 R. I., upwards of twenty years ago, and described in the Pro- 

 ceedings of this Academy (1858-59). He had repeatedly sought 

 for it in the vicinity of Philadelphia, but had never found it until 

 now. 



The development of the Cristatella in the locality indicated is 

 most remarkable and wonderful for its extent. Thousands of 

 vermicular groups spread over the bottom of the brook for about 

 twenty feet of length and a yard diminishing to a foot in breadth. 

 They invest all the submerged stones and plants, and are so closely 

 crowded as to intertwine with one another, leaving only narrow 

 intervals, without room for movement except by mutual displace- 

 ment. The groups are all attached to a common basal membrane, 

 from which, however, they are capable of separating themselves. 

 A large patch of the membrane covered with groups of the Cris- 

 tatella was raised and placed in a dish of water, and after a couple 

 of days most of the groups glided away from the membrane to 

 the bottom and sides of the dish. The basal membrane is amber 

 colored, homogeneous, and obscurely granular. A patch of it, 

 four inches long b}^ two and a half inches wide, closely covered 

 with groups of the polyp, preserved in alcohol, was presented as 

 a specimen for the museum. 



Jt would appear that in the development and growth of the 

 Cristatella groups, they from time to time break up into smaller 

 groups, and retain their connection only through the basal mem- 

 brane, which seems to be of an excrementitious character 



The basal membrane of the Cristatella was further interesting 

 from the circumstance that in the intervals of the groups of polyps 

 it harbored multitudes of Difflugia corona. 



