400 OSTRACE^E ; OYSTER ; ANOMIA. 



which thus accumulate, the race would speedily be extinguished 

 by the voracity with which Man preys upon them, were not the 

 destruction counterbalanced by the powers of multiplication 

 already noticed. But Man is by no means the only enemy to 

 the Oyster. Its body serves as food to many marine animals, 

 which have various methods of getting access to it, in spite of 

 its shelly defence ; from some of these it can secure itself by 

 closing its valves as soon as it is alarmed ; and against others 

 it has a more active means of defence, in the violent expulsion of 

 the water included between them, which (as it is itself fixed) 

 will frequently drive off its opponent. Various animals attack 

 it, also, by perforating its shell ; arid to these also it can offer a 

 passive resistance, by depositing new shelly matter within. So 

 that even this lowly-organised being, commonly regarded as one 

 of the most vegetative of animals, is provided by its Creator with 

 such means as are necessary for its preservation, and doubtless 

 also for its enjoyment. 



940. Nearly allied to the Oyster, but having also some- 

 points of resemblance to the class of Palliobranchiata or Brachio- 

 poda, is the genus Anomia ; which is 

 remarkable for the perforation of one 

 of its valves by a large aperture ; through 

 which a great part of the adductor 

 muscle passes, to be inserted into a 

 third plate (sometimes calcareous and 

 sometimes horny), by which the animal 

 adheres to foreign bodies. The valves 

 are thin and of irregular form ; being 

 influenced by the surface on which they 



FIG. 588. ANOMIA EPHIPPUJAJ. mi n x- j i j 



grow. Ihey are usually found attached 

 to the surface of other shells, especially those of Oysters. 



