142 MIGRATIONS OF MOLLUSCA. [CH. Ill 



state 498 days after its capture." This may serve as a 

 sample from a rich store of instances. 



Some aquatic Mollusca leave the water and travel over 

 the fields. This is the case for instance with Lymtwea 

 truncatula. Those that are not able in this way to travel 

 from pond to pond have to trust to vehicles which may be 

 animate or inanimate. Whirlwinds have been proved to 

 take up and deposit safely at a distance shoals of little 

 fish ; and not only fish but Mollusca a thundercloud at 

 Paderborn in Germany rained down crowds of the fresh- 

 water bivalve Anodonta anatina. More effective in ex- 

 tending the range of such Mollusca are birds and insects. 

 Canon Tristram on one occasion shot a mallard in the 

 Sahara to the feet of which were attached " the eggs of 

 some Mollusc probably Succinea." Mr Darwin proved by 

 suspending a duck's feet in an aquarium that the newly 

 hatched young of univalves will adhere, and might there- 

 fore be carried long distances. But on the other hand 

 there is little positive evidence that such a means of 

 transit is made use of in nature. Mr Kew enquired with 

 negative results from a large number of our leading 

 ornithologists whether shells had actually been found 

 adherent to the feathers or legs of birds. As a mere 

 matter of probability everyone is agreed that this method 

 of transit is feasible ; suggestions as to how it may take 

 place are unfortunately considerably in excess of records 

 of the actual event. Insects however have often been 

 taken with bivalve shells actually adhering to them ; "five 

 individuals at least," says Mr Kew, " of the water scorpion 

 (Nepa), a large flying bug, have been caught with shells 



