MEANS OF DISPERSAL. 4I 



water for any length of time ; one individual of A^. 

 suhsiilcata survived submersion for twelve hours, but 

 of a dozen kept in water, changed from time to 

 time, for five days, not one survived. It has been 

 pointed out, however, that these animals have calcare- 

 ous egg-capsules which are probably thick enough to 

 resist salt water, and these, as Mr. Edgar Smith has 

 remarked, if attached to floating timber, might be 

 carried to considerable distances.' 



Something, no doubt, may be attributed to the 

 agency of floating ice, for various kinds of shells have 

 been known to revive after having been frozen up. 

 Dr. Binney states that a Succinea " has been frozen in 

 a solid block of ice and yet escaped unharmed."^ 

 Anodonta cygftea and Paludina vivipara^ also, M. Joly 

 has observed, may be kept frozen up for some time 

 without being killed,^ and the latter has even produced 

 young after being thawed.'* In some thick ice which 

 Mr. W. A. Gain once removed from a stone trough or 

 " out-door aquarium," and allowed to melt slowly, were 



1 H. B. Guppy, " Solomon Islands," 1887, pp. 338-9 ; E. A. Smith, 

 " Proc. Zool. Soc," 1885, p. 588. 



"A. Binney, "Terrestrial Air-breathing Mollusks," i. (1851), 

 196. 



- On the other hand, however, it is stated that two specimens of 

 A. cygnea, exposed in the winter of 1 890-1, in an open vessel, to 

 the entire severity of the frost, were killed, their shells splitting 

 from dorsal to ventral surface on one side (see " Nature," xliii. 

 (1891), 464), and I have found several mentions of the fatal effects 

 of severe frosts upon bivalves in a state of nature. 



" " Comptes Rendus," xvi. (1843), 460, as quoted in "British 

 Conchology," i. (1862), xliv. 



