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 MOLLTTSKS 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 Mollusca 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 



VOL. m.-44. 



