TRANSPLANTATION OF BIVALVES. 69 



enough to carry shells, at least as large as 6*. corneum, 

 but they also furnish the much required proof of actual 

 overland transportal. No doubt the water-bugs above 

 mentioned are able to carry Pisidia of the size of 

 P.fontinale, as well as young Sphceria, but I have not 

 succeeded in obtaining any definite information respect- 

 ing their flying habits. Nepa is certainly a powerful 

 insect, and probably it frequently takes wing. Some of 

 our common " water-boatmen ^* {Notonecta, etc.) are 

 probably even stronger, and I have once or twice seen 

 them alight upon the surface of ponds in the sunshine, 

 fold their wings, and disappear into the water. 



From the facts now given, I think it may be safely 

 concluded that the local distribution of the smaller 

 bivalves has been influenced in a marked degree by 

 aquatic insects ; many isolated cattle-ponds, we may 

 feel sure, have been stocked with these molluscs by 

 chance visits from flying water-beetles and the like, and 

 as these occasionally stray out to sea or are blown to 

 great distances by gales, the facts have possibly a wider 

 significance : Mr. Darwin records that a ColymbeteSy a 

 water-beetle belonging to the Dytiscidae, once flew on 

 board the Beagle when forty- five miles distant from the 

 nearest land.^ 



Amphibia. 



Newts, frogs, toads, etc., it seems, often have their 

 toes caught by small bivalves : quite a number of 

 instances can be given ; a frog, in one case, had two 



1 « 



' Origin," p. 345. 



