THE OYSTER-INDUSTRY. 219 



■whoii an oyater-bed is formed and exists natnrally, all tlie conditions for its successfnl life are proljably iiresent, and any failure of au 

 important snp|ily would Ijo followed by a speedy extinction of all the oysters on the bed. Such determinations of the quality and 

 quantity of the food, character of bottom and water, and other matters, are only of interest and desirable for the puri)0se of comparing 

 one locality with another. Such was not the i)urpose of this investigation, and consequently the determination of those points has been 

 but incidental to the work. 



Probably the fecundity of a bed is increased to a certain extent by working upon it. The dredges or other implements used open 

 the bed and spread it, thus giving more room for development, and allowing a greater amount of food to reach the animals. The 

 mortality is great iu all thickly-populated tracts and in any closely-united community, and it is evident that the removal of any of the 

 brood-oysters could not be effected without destroying the fecundity of the bed, did not this very removal influence the mortality among 

 the young, so as to allow a larger number to come to maturity. But this removal of brood-oysters may become so great that the most 

 violent exertions of nature to supply others are unequal to the demand. It must also be evident, that as soon as the number of brood- 

 oysters is thus diminished, even to the slightest extent, the fecundity of the bed is impaired. 



This impairment constantly increases, influencing, as it does, both old and young. As the number of the latter decrease, so will the 

 number of the former, and as that number is again and again diminished, the number of young produced by them must constantly 

 diminish. Thus the cause for the destruction of the fecundity of the bed, and the gradual extinction of the animals upon it, can be 

 readily understood and as easily comprehended, as the fact that the fecundity and preservation of the productive powers of a bed depends 

 upon the number of mature, spawn-bearing oysters upon it. It is not meant by this, that none but the mature oysters iire capable of 

 reproduction, as such is not the case, oysters of even six or nine months' growth having been observed by mo with ripe ova and 

 spermatozoa in them, but the main dependence must be placed upon the adults in the community, as the spawn of the young growth is 

 not considerable when eom])ared with that of the other class. 



AVithout a knowledge of the number of oysters on a bed, it is impossible to say what number should be removed, and as an attainment 

 of the knowledge of the number on the bed is almost impossible, all that can be done is (o keep the proporlions between the young and 

 the mature as nearly the same as on natural beds, and this should be the aim and result of all laws having the protection of the beds in 

 view. 



Development of the OYSTER-snELL. — The way in wbich the oyster's shell is developed in the embrj"o, has 

 been shown by the quotations from Dr. W. K. Brooks' paper. It is increased with the growth of the oyster during 

 the warm months of the year, but receives few additions in winter. These are supplied by the delicately-fringed 

 mantle which, with the gills, forms the " beard " iu popular phra.se. From the ruffled edge of the mantle are 

 deposited very fine particles of carbonate of lime, till at last they form a substance as thin as silver-paper, and 

 exceedingly fragile. To these are added, more and more, until a satisfactory thickness and hardness is secured. 

 AVhen oysters are growing their shells they must be handled very carefully, as the new growth of the shell will 

 cut like broken glass ; it is said, al.so, that a wound on the linger from an oyster-shell is often very poi-sonous. 

 If this be true, it is probably owing to the minute organisms adhering to the shell, which are left in the wound 

 and i)n)duce a local fever. These shells are to the creatures they contain what his bones are to man. They 

 .su])port and protect the soft parts. Like the bones in the higher animals, they are composed of two substances, the 

 one animal, the other earthy. The animal part resembles gelatine; the earthy part is principally carbonate of lime. 

 They contain, however, small quantities of phosphate of lime, a little potash, and soda and acid. In one hundred 

 parts of ojster-sliells there will be found — 



Water 17 



Animal matter 2 



Carbonate of lime 75 



Phosphate of lime 3 



Other salts 3 



100 



Materials for the growth of the shell. — The materials for its shell, like its food, are supplied by the 

 sea-water; and w-here, by reason of there being a scarcity of these ingredients in the shores of the sea, the water 

 at any one place lacks them, or is feebly supplied, oysters will not flourish, or will produce light and ea.sily-broken 

 shells. Such was the case on Nantucket. " If the shell is thin, or if it is formed very slowly, the danger from 

 enemies and accidents is greatly increased; and those oysters which are able to con.struct their shells with the 

 greatest rapidity, are the ones which survive and grow up. The amount of dissolved carbonate of lime which the 

 ocean contains is unlimited, but the amount which can reach each oyster is not very great ; and if all the oysters 

 which attach themselves were to survive, there can be no doubt that they would exhaust the available supply of 

 lime before they failed to obtain enough organic food." It is well known to (-ouchologists that coral reefs and 

 limestone islands are richest in all sorts of mollusks ; and one reason, no doubt, why the young oysters thrive best 

 on the natural oyster-bed is, that the old dead shells are soon corroded, and in a few years entirely dissolved, by 

 the sea-water, affording an abundance of new shell-material for the survivors. Tlie vast amount of dissolveil lime 

 poured into the Gulf of Mexico by the Mississippi and other rivers, doubtless largely accounts for the abundance 

 of niollusks, marine worms, and radiates that throng in its waters. Varying conditions will cause much difference 

 iu the shells of oysters from various localities. Naturalists at tirst thought these differences amounted to specific 

 distinction, and experienced dealers can pick out oysters from different regions not only, but from difterent beds in 

 the same region. Mr. Win.slow notes that, in the Chesapeake, oy.sters found upon beds that have l)cen much 

 worked differ materially, being single and broader, in conipari.son to their length, round und witli l^liint liills. 



