NATURAL SCIENCES OF PHILADELPHIA. 139 



August 18. 

 The President, Dr. Ruschenberger, in the chair. 

 Fourteen members present. 



August 25. 

 -The President, Dr. Ruschenberger, in the chair. 

 Twenty members present. 



On Pectinatella magnijica. Prof. Leidy exhibited a living 

 specimen of the fresh-water ciliated polyp, formerly described by 

 him under the name of Pectinatella magnifica. It was obtained 

 by him this morning from the mill-pond at Kirkwood, N. J., on 

 the Camden and Atlantic R. R. The specimen, about four inches 

 square and three inches thick, is a fragment of a large colony, 

 which enveloped the submerged trunk of a tree. The entire 

 colony was estimated to be about six feet long, and from six to 

 twelve inches in diameter, including that of the tree trunk, which 

 was about four inches. Several branches of the tree were also 

 invested with extensions of the colony from six inches to a foot 

 in length. Pectinatella is by far the largest of all the known 

 fresh-water ciliated polj-ps, and, indeed, is not surpassed b}^ any 

 of the marine forms known to us. It has not been determined 

 whether the huge Pectinatella colonies start each from a single 

 individual, or are the result of the confluence of a number of 

 small colonies. On the approach of winter the colonies die and 

 undergo decomposition, in which process the remarkable winter 

 eggs or statoblasts are liberated. These are provided with 

 anchor-like spines, by which, as in the case of the eggs of skates 

 and sharks, they become attached to various fixed bodies. 



On a Pay^asitic Woy^m of the House-fly. Prof. Leidy remarked 

 that since it had become well known that manj^ parasitic worms 

 passed different stages of development within several different 

 animals, he had from time to time sought for the sources from 

 whence the more common thread worms obtained entrance into 

 the human body, but thus far without success. The Trichina 

 spiralis, discovered in man in 1833 by Mr. Hilton, and described 

 and named by Prof. Owen in 1835, was first found in the hog by 

 Prof Leidy in 1846 (See Proc. A. N. S., iii. 108), but it was not 

 until some years subsequently that it was determined that man 

 and the hog acted reciprocally as hosts for the Trichina in its 

 different stages of development. 



