6 



SHELL GALLERY. 



Hiberna- 

 tion and 

 torpidity. 



Economic 

 uses. 



Geological 

 history. 



much longer time. Some of the marine forms live for a considerable 

 period, the Common Oyster not attaining full-growth until about 

 five years old, after which it may continue to live for many years. 

 The Giant Clam, a specimen of which is placed on the floor near 

 the entrance to the Gallery, must, one would think, have a very 

 long existence, judging from the size and thickness of the shell. 

 All terrestrial mollusks hibernate in cold climates, hiding them- 

 selves away in the ground between roots and similar sheltered places. 

 In tropical countries some assume a state of torpidity (activate) 

 during the hottest and driest season of the year, closing up the aper- 

 ture of their shells with a temporary lid or door (epiphragm), in order 

 to resist the dryness of the atmosphere. Some of these " summer- 

 sleepers" are endowed with a remarkable tenacity of life. An 

 Australian Pond-Mussel has been known to live a year after being 

 removed from the water; several Land-Snails have revived after a 

 captivity of from two to five years, without any food whatever. 

 One of the most remarkable instances of this kind occurred in the 

 British Museum. A specimen of Helix desertorum, a common 

 Desert-Snail from Egypt, was fixed to a tablet in March 1846, and 

 in the same month of the year 1850 it was discovered to be alive. 

 It must have come out of its shell in the interval, and finding it 

 was unable to crawl away, had again retired within it,* closing 

 the aperture with a new epiphragm, but leaving traces of slime 

 upon the tablet, which led to its immersion in water and subse- 

 quent revival, having passed a period of four years in a dry museum 

 without the smallest particle of food. 



The economic uses of mollusks to man are manifold, and will be 

 mentioned in the course of the description of the several families ; 

 but here may be the place to direct the attention of visitors to 

 Table-cases E & H near the entrance of the room, containing 

 some specimens of articles manufactured from shells, such as 

 cameos, flowers, bracelets, brooches, &c. 



Mollusca made their appearance on the globe at a very early 

 epoch in the history of the development of animal life, a large 

 number of fossil forms, such as Nautilus, Lituiies, Orthoceras, &c., 

 being found in the oldest Palaeozoic formations. Probably all these 

 belonged to the Tetrabranchiata, of which one descendant only, the 

 Pearly Nautilus, has survived to our period. Some Gastropods 



