50 PEARLS [CH. 



monsoons and storms. The oysters are buried — 

 young oysters are destroj^ed, and in some cases the 

 destruction is enormous. Herdman and Hornell ob- 

 served the loss of "thousands of millions" of young 

 oysters from this cause in a year. On some of the 

 paars this depletion seems to be of regular occurrence 

 every year. 



Next we come to the natural enemies of the 

 mollusc, and they are numerous, though probably 

 only a few commit serious damage. The " black- 

 listed " animals are in the first place the fishes which 

 devour oysters. They are chiefly skates and rays of 

 diiFerent species, and the file-fishes. The large rays, 

 up to a dozen or more feet across, have been observed 

 feeding upon the shellfish. With their broad-surfaced, 

 specially adapted crushing teeth they can make short 

 work of the delicate shells ; and shell fragments, the 

 result of their depredations, are often numerous. The 

 file-fishes feed upon immature oysters. 



The next group of enemies is that of the molluscs 

 which bore into shells. The gastropoda (univalves 

 like the common whelk of the English coast) are 

 provided with a proboscis armed with a chitinous 

 file. In addition, however, to boring holes by this 

 means and then inserting the proboscis, it is quite 

 certain that many of these univalves either catch an 

 unsuspecting bivalve with its shell open, or drive part 

 of their shell between the valves of their prey and 



