S48 INTRODUCTION TO CONCHOLOGY. 



conscious also that something exists exterior to themselves. 

 They choose^ reject, and vary their operations with judg- 

 ment, defend themselves by adequate and complicated 

 means, repair their losses, and occasionally assume new 

 habits. They possess, when young, the faculty of swimming 

 by means of a simple yet admirable development of their 

 powers; but, when arrived at full growth, this faculty or 

 inclination ceases, and while some of their active relatives 

 are darting round them, they remain contentedly in their 

 places of abode, surrounded by a numerous and continually 

 increasing progeny. When, however, they incline to move, 

 they contrive to bolster themselves up on one side, till they 

 stand nearly upright ; and then, availing themselves of the 

 flowing or ebbing of the tide, they open their shells and are 

 tossed over by the pressure of the water. In this respect 

 they differ materially from many of their brethren. 



The common Oyster is too well known to render descrip- 

 tion necessary. Britain was celebrated for this species as 

 far back as the time of Juvenal, who, satirizing Montanus, 

 a noted epicure, says of him — 



" He, whether Circe's rock his oysters bore, 

 Or Lucriue's lake, or distant Richborough's shore, 

 Knew at first taste." 



