406 MYTILACE2E ; LITHODOMI ; DREISSENA. 



cases have not been uncommon. Whilst Mussels in general 

 attach themselves to the surface of rocks, &c., others appear to 

 seek out hollows, and imbed themselves there. Others form ex- 

 cavations for themselves in mud ; and are found in spots which 

 are occasionally left dry by the tide. 



1031. The Lithodomi are endowed with the power of per-" 

 forating stone and masses of coral, as well as large shells of other 

 Mollusca. In the earlier stages of life, it is stated by Cuvier, 

 the Lithodomi suspend themselves by their byssus ; but when 

 they have pierced the bodies to which they are attached, and 

 introduced themselves into the cavity, the byssus disappears. 

 The excavation does not seem to be here produced by the 

 mechanical action of the shell, which is not adapted for such an 

 office. Nor is there any reason to believe that it is occasioned 

 by a solvent fluid secreted by the animal. It is attributed by 

 Mr. Garner principally to the currents of water constantly im- 

 pelled against the rock by the vibration of the cilia ; and in this 

 supposition there is much probability. The lithodome Mussels, 

 as well as others, are used as food where they abound ; and 

 means have been taken on some parts of the coast to cause them 

 to multiply. As with Oysters, it appears that the Mussels are 

 rendered more tender, and the quality of their flesh improved, 

 by putting them in places where the saltness of the sea-water 

 is tempered by rain or river-water. Accordingly, on the coasts 

 of France and Italy, regular breeding-places have been estab- 

 lished, where those which have been obtained from the sea are 

 cast for a time to improve their quality, and where also the 

 spawn is reared ; these are so arranged as to communicate with 

 the sea, but to allow the intermixture of fresh water at pleasure. 



1032. A Mollusk allied to the Mussel, the Dreissena poly- 

 morpha, has been recently introduced into this country ; and 

 affords an interesting example of the complete naturalisation and 

 rapid multiplication of a foreign species. This is evidently due 

 to the variety of circumstances under which it can exist. It is 

 found abundantly in the Black Sea, the Baltic, and other inland 

 seas ; and it lives, like the Mussel, in aggregated masses, attached 

 to the bottom by the byssus. It is also found in many of the 



