18 MANUAL OF THE MOLLUSCA. 



or periodic moutlis QdI. III., fig. 3), to liave lived and continued 

 growing for many years. 



Many of the bivalves, like the mussel and cockle, attain their 

 full-growth in a year. The oyster continues enlarging his shell 

 by annual " shoots," for four or five years, and then ceases to 

 grow outwards ; but very aged specimens may be found, especi- 

 ally in a fossil state, with shells an inch or two in tliickness. 

 The giant- clam ftridacnaj, which attains so large a size that 

 poets and sculptors have made it the cradle of the sea-goddess. — 

 must enjoy an unusual longevity ; living in the sheltered lagoons 

 of coral-islands, and not discursive in its habits, the corals grow 

 up ai'omid, until it is often nearly buried by them ; but although 

 there seems to be no certain limit to its life (though it may live 

 a century for all that we know), yet the time will probably come 

 when it will be overgrown by its ueighbom-s, or choked with 

 sediment. 



The firesh-water moUuscs of cold climates bmy themselves 

 daring winter, in the mud of then- ponds and rivers ; and the 

 land-snails hide themselves in the ground, or beneath moss and 

 dead leaves. In warm climates they become torpid dming the 

 hottest and driest pai-t of the year. 



Those genera and species which are most subject to this 

 " summer sleep," are remai'kable for their tenacity of life ; and 

 numerous instances have been recorded of their importation from 

 distant countries, in a living state. In June, 1850, a li\dng 

 pond-mussel was sent to ]\Ir. Gray, from Australia, which liad 

 been more than a year- out of water.* The pond-snails (ampul- 

 larice) have been found alive in logs of mahogany from Hondm-as 

 (Mr. Pickering) ; and M. Caillaud carried some from Egypt to 

 Paris, packed in saw-dust. Indeed, it is not easy to ascertain 

 the limit of their endm-ance ; for Mr. Laidlay having placed a 

 number in a drawer for this purpose, found them alive after Jive 



* "It was aUve 498 days after it was taken from tlie pond; and in the 

 interim had been only twice for a few hours in water, to see if it was alive." — 

 Rev. W. 0. Newnham. 



