39 



The oyster is a mollusc or bivalve shell- 

 Q ter ? a fish ' thonging to the genus ostrea, sub- 

 class monomva, as it has only one 

 adductor muscle for closing the two halves of the valve or 

 double shell. It is a soft, cold-blooded, invertebrate animal, 

 without any internal skeleton. The shells are composed of 

 carbonate of lime with a small admixture of animal matter. 

 Unlike many molluscs, it has no foot or locomotive organ, 

 though occasional motion may be attained by rapid 

 expulsions of water. At least a hundred different species 

 are known to the naturalist in all parts of the world, at 

 varying depths ; and going back to such an early period of 

 geology as the palaeozoic, remains of the oyster are found 

 in great variety, all of which are believed to have descended 

 by evolution from one common ancestor, which lived in so 

 remote an age that the mind can scarcely realise it. I have 

 lately seen a large number of fossilized oysters found during 

 the recent excavation for the new Staines reservoirs. At the 

 same place were discovered several specimens of the 

 Xa u til us, still retaining the beautiful external pearly surface. 



For the marvellous structure of the oyster there is no 

 space in these notes, though passing reference must be 

 made to one of its organs, the gills, which fulfil many more 

 offices than those of the fish for instance. In the oyster 

 they are a breathing organ. They purify its blood and 

 keep up a circulation cf water. They gather up food from 

 the water and carry it to the mouth. They are also repro- 

 ductive organs, and brood chambers, and carry out all 

 these duties in the most wonderful way. Thanks to the 

 painstaking investigations of Dr. Brooks and Lieutenant 

 \Vinslow in America, to M. Bouchon-Brandeley in France, 

 and to other scientists at home and abroad, we can under- 

 stand things about the oyster which seem to have been a 



