Ixvi INTRODUCTION. [CH. 



in marine bivalves the attacks of perforating annelids, 

 would be sufficient inducements for the shell -fish endea- 

 vouring to smother or keep out its assailants by secre- 

 tino- an extra quantity of nacreous matter. The nucleus 

 of many pearls reveals the origin of their formation. A 

 communication made by Signor Antonio Villa in 1860 

 to the Literary and Scientific Athenaeum at Milan (en- 

 titled ''Suir origine delle perle''), and another by Mr. 

 Robert Garner to the Linnean Society in December 1861 

 (''Note on the formation of pearls''), will well repay a 

 perusal by those who are interested in this curious sub- 

 ject. The unsuccessful experiments made a century ago 

 by Linne for the artificial production of pearls by the 

 Unio margaritifer in the rivers of Sweden (and for which 

 he took out a patent), and the ingenious process invented 

 by the Chinese, of putting little josses or images of some 

 incorrodible metal between the mantle and shell of an- 

 other freshwater mussel, so as to have them coated over 

 with several layers of pearly matter, are now well known. 

 Great quantities of the Mytilus edulis are said to have 

 been collected a few years ago in the estuary of the 

 Conway, as well as in the North of Ireland, and exported 

 on account of the Jews, for the purpose of fabricating 

 mock pearls out of their nacreous linings. 



Another testaceous article of commerce in this coun- 

 try for ornamental purposes is the " ormer " or ear-shell 

 (Haliotis tuberculata), which is found abundantly in the 

 Channel Isles. Many tons of these shells are annually 

 gathered for the Birmingham market ; and their inner 

 coats of mother-of-pearl are sufficiently thick to make 

 buttons and studs, or for inlaying. 



Shells of various kinds are collected wholesale from 

 the famous beach of the islet of Herm, and sent to 

 England for fancy-work. The Romans used shells for 



