420 THE LIMA, OR FILE-SHELL. 



regular rows like the tiles of houses, and are at all times ready to be taken from the 

 bed and sent to market. 



This process possesses a double value, inasmuch as an oyster-bed, if left to itself, 

 would increase to such an extent as to endanger navigation ; and these inland banks 

 are always accessible, whatever may be the weather. In some cases, when confervoid 

 growths are rife, the Oysters attain a decided green hue, and are thought very valuable 

 by connoisseurs in such matters. In all improvements, however, there is always some 

 drawback. The Oysters produced by artificial culture are acknowledged to be fatter 

 and finer than those which are suffered to grow in the open seas ; but their artificial 

 size is said to be a poor compensation for their comparative want of flavor, the artificially 

 bred Oyster being to the marine mollusc what the capon is to the pheasant. 



In the sea, thousands of Oysters perish by the attacks of a strange enemy. The 

 reader has doubtlessly remarked that the shells of many Oysters are partially perforated 

 by little round holes. These are the marks left by a kind of sponge, called Cliona, 

 which burrows into and gradually destroys the shells of this mollusc, causing them to 

 fall to pieces by its ravages. 



In the center of the engraving on the previous page is seen a species of the genus 

 Ostrea, which is remarkable for its very long hinge. 



THE uppermost figure represents the CHINESE WINDOW-SHELL, a curious and rather 

 valuable shell, which is found in the country from which it takes its name. 



This shell is extremly flat, and of a beautiful translucence, and in many parts of 

 China is employed for windows, just as is ground-glass among ourselves, the nacreous 

 substance permitting the light to pass through, but effectually preventing an inquisitive 

 eye from distinguishing objects within the apartment. Very small pearls are found in 

 this shell, too minute and too opaque to be employed by jewellers. They are, however, 

 collected and exported to India, where they are calcined and formed into lime for the 

 use of wealthy betel chewers. They are also burned in the mouths of the dead. 



The shell is of great use in commerce, affording the substance from which is cut 

 those large flat " pearl " buttons that were formerly so fashionable, but seem now to 

 have descended to the denizens of the stable. The button " moulds " are cut from the 

 shell by an instrument that somewhat resembles the trephine, by which portions of the 

 skull are removed in case of severe injuries, and in their rough state look like gun- 

 wads. They then pass through a series of processes in which they are polished and 

 pierced, and made ready for sale. 



THE lowest figure represents the SADDLE-SHELL, remarkable for the way in which the 

 shell is attached to other substances. Two specimens may be seen in the illustration 

 placed on an oyster. The contrivance by which it is attached is most remarkable. 

 The animal deposits a plug or peg of shelly matter on the oyster, and in the right valve 

 there is a hole or notch into which the peg fits, much after the fashion of a button. 

 When the left valve is in its place, this contrivance is hidden. The shell of this 

 creature is beautifully thin hardly thicker, indeed, than the paper on which this 

 account is printed and elegantly waved. It inhabits the British seas. 



THE three objects in the accompanying illustration represent different views of the 

 same species. 



The LIMA, or FILE-SHELL, is worthy of notice on account of the curious refuge which 

 it constructs by binding together a large mass of shells, corals, sand, and other materials, 

 by means of the silken threads or "byssus " which it is capable of secreting. On the 

 left hand is seen a specimen almost entirely buried in the mass of nullipores which it 

 has gathered around its shell. The upper figure on the right hand exhibits the same 

 shell as it appears when free and in the act of swimming. The long tentacular 

 appendages are kept in constant movement, possibly without the will of the animal, 

 keeping up their writhing contortions just as our hearts continue to beat without our 

 knowledge. Even after the death of the animal, and when they have been separated, 

 the filaments continue to move, twining and twisting like so many worms. 



