36 THE DISPERSAL OF SHELLS. 



ning water," ' and in an old canal north of Inchbroom, 

 Mr. Martin " is said to have seen hundreds of snails of 

 this species sailing from one end of the canal to 

 the other, resembling " a fleet of herring-boats in 

 miniature." In a pond in Yorkshire, Mr. Christy ob- 

 served that this snail often crawled on the top of the 

 duckweed in mild weather and was liable to be blown 

 to one end of the pond by the breeze in large 

 numbers;^ The free-roving larvae of Dreissena^ for a 

 time, live chiefly near the surface of the water, and, as 

 Dr. Korschelt observes, are likely to be carried forward 

 for long distances by currents/ Univalves frequently 

 attach their eggs to loose leaves and sticks in the 

 water, and these, as Sir C. L}'ell states, " are liable 

 to be swept away, during floods, from tributaries to the 

 main streams, and from thence to all parts of the same 

 basin ;" a species, it is added, might thus migrate during 

 one season from the head-waters of the Mississippi, or 

 any other great river, to countries bordering the sea at 

 the distance of many thousands of miles. Figures given 

 by Lyell show the ova of an Aiupullaria fixed to a 

 small sprig which had fallen into the water, those of a 

 Plaiiorbis attached to a dead leaf, and those of a Liinncsa 

 adhering to a dead stick/ In a pool in Epping Forest 

 I recently saw " egg-jellies " of LiinucBa auricularia 



1 "Topography and Nat. Hist, of Lofthouse," 1882, p. 242. 



' Quoted by the Rev. G. Gordon, "Zoologist," xii. (1854), 4457. 



3 R. M. Christy, "Zoologist," (3), v. (1881), 184. 



^ E. Korschelt, "Ann. and Mag. Nat. Hist ," (6), ix. (1S92), 166. 



° " Principles," ii. p. -^Zo, fig. 142. 



