MEANS OF DISPERSAL. 4S 



Animals of various kinds, it can hardly be doubted, 

 are actively engaged in dispersing shells. The "short 

 and frequent migrations from pond to pond or from 

 stream to stream," to which Mr. Darwin has alluded, 

 have, almost certainly, been largely brought about by 

 birds and other creatures, and transportal by such 

 agency over considerable tracts of ocean, it has been 

 shown, is at least possible. Many birds^ fish, amphibia, 

 etc., swallow large numbers of shells, which are sure, in 

 some cases, to survive for a time in their stomachs ; 

 thus, for instance, Mr. Baker Hudson has often found 

 living Pisidia, with their valves tightly closed, in the 

 stomachs of frogs, and this, of course, suggests a possi- 

 bility that sudden deaths of shell-eating creatures, 

 brought about by birds and beasts of prey, may have 

 led, at rare intervals, to the setting free of living shells 

 in spots considerably removed from their original 

 homes ; and some birds, it is important to notice, on 

 being frightened or wounded, occasionally or habitually 

 cast up the contents of their crops. That shells are 

 voided in a living state with the excrement seems less 

 likely, for they are almost sure to be killed during their 

 passage through the digestive organs. No less a person 

 than Dr. Kobelt, however, has ventured to express the 

 opinion that small mussels and even sometimes opercu- 

 late water-snails, when swallowed alive by birds, may 

 possibly pass the intestines unhurt/ Experiments on 



was drawn up by a passing tornado, and afterwards deposited 

 its living burden at the place in question." 



W. Kobelt, " Fauna der Nassauischen Mollusken," 1S71, p. 14. 



