340 ANNUAL OF SCIENTIFIC DISCOVERY. 



would not be washed off their feet. When making land they would 

 be sure to fly to their natural fresh-water haunts. I do not believe 

 that botanists are aware how charged the niud of ponds is with seeds. 

 I have tried several little experiments, but will here give only the 

 most striking case : I took in February three table-spoonfuls of mud 

 from three different points, beneath water, on the edge of a little 

 pond; this mud, when dried, weighed only six and three-quarter 

 ounces ; I kept it covered up in my study for six months, pulling up 

 and counting each plant as it grew. The plants were of many kinds, 

 and were altogether five hundred and thirty-seven in number ; and 

 yet the viscid mud was all contained in a breakfast-cup. Considering 

 these facts, I think it would be an inexplicable circumstance if water 

 birds did not transport the seeds of fresh-water plants to vast distan- 

 ces, and if consequently the range of these plants was not very great. 

 The same agency may have come into play with the eggs of some of 

 the smaller fresh-water animals." 



In connection with these statements of Mr. Darwin, the following, 

 from the Proceedings of the Philadelphia Academy, will be read with 

 interest : 



Mr. Lea mentioned that he had recently received a letter from Dr. 

 Showalter, of Uniontown, Alabama, in which he mentions that speci- 

 mens of Physa (gyrina) Say, which he sent on, were obtained in an 

 open neglected cistern, and in a trough of water supplied by an ar- 

 tesian well ten miles from the town. Dr. Showalter expressed his sur- 

 prise that these Physce should find their homes so soon at these 

 artesian wells. There are no streams or pools near to these wells, 

 but in a few years after they are bored, and water supplic-1. these 

 shells may with certainty be found. Mr. Lea went on to mention 

 that he had, nearly thirty years ago, found an undescribed species of 

 Lymncea, accompanied by Physa heterostropha Say, in a small arti- 

 ficial pond on the high grounds near to the Falls of Schuylkill, about 

 four miles north of Market Street, now within the limits of this city. 

 He published an account of it in April, 1834, in the Transactions of 

 the American Philosophical Society, under the name of acuta. The 

 pond was small, and dug out, for one and one-half to two feet deep, 

 simply for the supply of rain-water for cattle. Afterwards it dried 

 up, and the shells were no longer to be obtained there. He never 

 found this Lymncea in any other habitat; but many years subse- 

 quently, Dr. Ingalls, of Greenwich, N. Y., near to Lake Champlain, 

 sent him several specimens of what he regarded as a new Lymncea, 

 but which was at once recognized as the acuta, heretofore found only 

 in the one habitat near the Falls of Schuylkill. In the minds of some 

 zoologists a difficulty exists as to the existence of species in such con- 

 stricted, isolated points as mentioned above, but that difficulty, in Mr. 

 Lea's mind, was done away with under the belief that very young 

 mollusks may be transported on the feet of birds from distant points, 

 or on those of cattle going to drink from one place to another. 



CEREBRAL SYSTEM OF CLASSIFICATION OF THE MAMMALIA. 



In a lecture recently given before the Royal Institution, London, 

 Professor Owen stated that the lowest forms of mammals possess 



