352 Professor Huxley [May 11, 



sent, unfit for their support ; and the east coast of Schleswig, washed 

 by its brackish waters, is devoid of oysters, while certain parts of the 

 west coast are famous for their oyster beds. Gravel, stones, and dead 



gliells commonly known as " cultch " — form the most favourable 



bottom, as they facilitate the attachment of the young. Disturbed 

 muddy bottoms, on the other hand, are fatal, for reasons which have 

 already been given. But it is a curious fact, that even where a large 

 extent of sea-bottom presents apparently the same conditions, oyster 

 beds occur in some localities and not in others. 



The struofrle for existence is as intense in the case of the passive 

 oyster as in that of the most active of animals. Oyster competes 

 against oyster for the common store of food suspended in the water, 

 and for the dissolved carbonate of lime out of which the shell must 

 be made. Innumerable other animals, sponges, corallines, polypes, 

 tunicates, other bivalve mollusks, especially mussels and cockles, live 

 in the same way and abound on oyster beds, often attached to the 

 shells of the oysters. Prof. Mobius counted as many as 221 distinct 

 animals of various species on one oyster shell. All these compete 

 with the oyster for food, while, on the other hand, they may 

 occasionally supply food to the oyster in the shape of debris, and, 

 perhaps, of their eggs and microscopic larvce. 



From birth onwards oysters are the prey of many animals. The 

 minute larvae, as they swim about, are probably swallowed by every- 

 thing which has a mouth large enough to admit them ; and, as soon as 

 the young oysters have become sedentary, they are eaten by every- 

 thing which has jaws strong enough to crush them. Ground fishes, 

 such as rays and fish of the cod tribe, easily break them up when they 

 have grown much larger ; while starfishes swallow them whole. Even 

 the half-grown oyster, with a shell strong enough to resist most teeth, 

 and too big for the maw of an ordinary starfish, is not safe from the 

 depredations of the dogwhelk (Purjjura Icqnllus) and the whelk tingle 

 (Murex erinaceus), which efiect a burglarious entrance, by means of 

 the centre-bit with which nature has provided their mouths. It is 

 very curious to watch a dogwhelk perched upon an oyster shell and 

 patiently working, hour after hour, until the little and apparently 

 insignificant tunnel, by which the insidious enemy will get access to 

 the fat prey within, is completed. If you pull him ofi", he puts on as 

 soft a look as the most innocent snail could do, as who should say, 

 " Why prevent me from establishing closer intercourse with the dear 

 neighbour at the other end of my tunnel ? " The guardians of the 

 oyster, however, who have not much of the " friend of humanity " 

 about them, ruthlessly arrest the operations of the tunnellers by 

 sudden squash with boot or hammer. And well they may, for they 

 have few more dangerous adversaries. In the Bay of Arcachon, 

 14,000 whelk tingles were picked off 100 acres of oyster ground in the 

 course of a month. 



Other animals injure the oyster indirectly by mining in the shell. 

 The boring sponge, Cliona^ does this ; and a very curious instance of 



