THE COMMON OYSTER. 345 
between the valves. The substance of the shell is rather soft and perforated. The valves are 
slightly open at each end, and blunted in front. Very little is known of its habits in the 
living state, but it is worthy of notice that the Goose-bill Lamp-shell is the oldest known form 
of organic life. 

ACEPHALA. 
THe HEADLESS MOLLusKs are the lowest in rank in the scale of life. The common Clam 
is a good example of the class. The long fleshy process of the Clam is popularly called the 
head, but it is the foot, in one sense, being.opposite the place where the head would naturally 
be. The true foot is midway, and is the tougher triangular part which is the locomotive 
organ. The long fleshy part which is called the head consists of two tubes, one cavity absorbing 
water and the other throwing it out after it has served its purpose. 
In some of the bivalves, the mussel, for example, there is a gland near the foot which 
secretes the byssus, a bundle of threads by which the animal fastens itself to any object. 
Bivalves are hinged, and re-enforced as it were by a stout ligament on the outer side. 
One or two adductor muscles are placed within, attached to each shell within the depressed 
portion that shows on the inside of the bare shell. The ligaments, by contraction, tend to 
force open the shell’s valves ; the muscles on the inside draw them tightly together. 
Classification of J/ol/usca is yet in a very unsatisfactory state. As in the case of some 
other divisions of natural history, as long as there is no satisfactory guide to classifying, a 
consideration of the forms under family heads is most convenient and useful. 
Though not possessing so many species as the gasteropoda, this group surpasses it in point 
of numbers, the bivalves being produced in countless myriads, and, perhaps, less exposed to 
the attacks of foes than most of the race. They are extremely useful in both salt and fresh 
water, feeding on the particles that would otherwise pollute the element in which they live. 
Their mode of feeding is somewhat similar to that of the last-mentioned group, the water 
being driven over the mouth by the continual action of certain appendages, and there cleared 
of all its solid portions. So completely does a bivalve effect this purpose, that it even inter- 
cepts the microscopic plants and animals which are invisible to the naked eye, and conveys 
them to the stomach with marvelous certainty. 
In the first family, of which the common Oyster is a very familiar instance, the two 
valves are unequal in size, and the animal inhabits the sea. The Oyster is too well known to 
need description ; but it may be mentioned, that the practical naturalists have for some years 
been carefully studying its habits, for the purpose of breeding the valuable mollusk artificially, 
and so of securing a constant supply throughout the four months of the year during which the 
creature is out of condition. In this country the system is being gradually carried out, but in 
France it is developed to a very large extent, and with great success. 
The details of the process are too elaborate to be here described, but the general idea may 
be given in a few words. The very young spawn, or “‘spat,’? as it is technically named, is 
removed from the natural beds, and is dispersed in shallow ‘‘ banks,’’ so that each tiny Oyster 
has plenty of room, and can affix itself to the bed of the bank without being injured by the 
pressure of its fellows. Fascines, made of slender branches, and sunk into banks paved with 
stone, birch, and broken earthenware, are found to be most useful for this purpose. In the 
banks near Dieppe, the Oysters are seen lying in regular rows like the tiles of houses, and are 
at all times ready to be taken from the bed and sent to market. 
This process possesses a double value, inasmuch as an oyster-bed, if left to itself, would 
increase to such an extent as to endanger navigation; and these inland banks are always 
accessible, whatever may be the weather. In some cases, when confervoid growths are rife, 
the Oysters attain a decided green hue, and are thought very valuable by connoisseurs in such 
matters. In all improvements, however, there is always some drawback. The Oysters pro- 
duced by artificial culture are acknowledged to be fatter and finer than those which are suffered 
Vou. TT.—44. 
