珍珠是怎么形成的?翻译成英文
发布网友
发布时间：2022-04-23 05:42
共4个回答
热心网友
时间：2023-10-17 00:18
当蚌在海床进食中，贝壳张开，沙粒，寄生虫等异物偶尔掉进去，外套膜受到刺激，它就会分泌出珍珠质，把掉进去的异物层层裹住，使其圆滑，逐渐形成珍珠囊－也就是珍珠光亮润泽的外层。
因此，所形成的珍珠是圆球形或非圆球形，关键在于珍珠质能否均匀地在刺激源周围积累。
When the mussels take food on the seabed with its cameo shell open,sand,parasite and so on eyewinker drop into the cameo shell by accident,then the pallium suffer shock so that it will secrete nacrum to muffle the eyewinker drop into it to make the eyewinker smooth and evasive to graally form pearl sac---that's the bright and smooth outerlayer of an pearl.
Therefore,whether the forming pearl is round or not depends on whether can the nacrum evenly accumulate around the stimulus.
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热心网友
时间：2023-10-17 00:18
The pearl is an animal proct secreted by certain shell mollusca, of which one kind live in the sea, and the others in fresh water. Pearls are quite common, but those which have considerable dimensions, joined to a regular form and beautiful reflections, are rare and of high price.
Formed almost exclusively of lime and of an organic matter, the pearl is very easily acted on; as regards resistance, it has nothing in common with precious stones, even those most easily destroyed.
The pearl was dedicated to Venus. It is sacred to love and beauty. In the "marriage of Cupid and Psyche"-a fine engraving upon sardonyx, wherein the figures are enveloped in transparent veils, a work of great difficulty in engraving upon stone-the lovers are united by a string of pearls-emblem of conjugal bonds-by aid of which the god Hymen, bearing a torch, concts them to the nuptial couch (Fig. 83).
A number of opinions have been expressed upon the origin of the pearl. The ancients poetically ascribed it to a drop of dew falling at morning or evening into the opened shell.
"Brighter the offspring of the morning dew,
The evening yields a skier birth to view."
It was once a common belief that the pearl was a morbid proction of the animal. Above all, it has been thought that it originated in some foreign substance, such as a grain of sand, or an animal parasite, introced accidentally into the shell. This substance, it was supposed, tortured the animal, which, to free itself from the irritation, covered it with a pearly secretion. Acting on these ideas, the Chinese are said to have obtained pearls artificially, by piercing the shell, and slightly wounding the animal.
There is probably some truth in these hypotheses; but an examination of the pearl under the microscope proves that such modes of formation are not the only ones employed; and even that they do not necessarily enter into the formation of these beautiful proctions. Indeed certain pearls show in their interior spherical cavities perfectly empty; and others, which are completely solid to the centre, display in all their parts a regular and continuous texture, without the least trace of any foreign matter.
A pearl of the first quality should possess, above all things, a fine orient, or water. By this expression is meant a pure whiteness, joined to a lively lustre that sparkles in the light. There are pearls, too, which, with a white colour, show a delicate reflection of azure. These are the most highly esteemed.
The second quality of a fine pearl is, that it should be perfectly spherical, or regularly pearshaped.
There are a great number of pearls whose colour has a yellowish tinge. This alone is a mark of inferior quality.
It is very probable that pearls possessing this yellowish shade exist normally in the shell. Tavernier, however, thinks that all pearls are white, and that the yellow tint is inced by putrefied procts, resulting from the treatment of the shells in their places of proction; the pearl-shells being left in the open air that they may open of themselves after the death of the animal. The work is thus accomplished without any expense, and without risk of breaking the pearls, an accident that occurs very frequently if the shells are opened artificially. In support of his theory Tavernier states a fact, which, if established, would be conclusive; which is, that yellow pearls are never found in shells that have preserved their water.
The shells in which pearls are found belong to several families of the large class of mollusca; but the most important of all is the--
Avicula margaritifera, Bruguiere; Pentadina margaritifera, Lamarck. This species not only proces the pearl, but furnishes to commerce vast quantities of mother-of-pearl of the kind most valued.
There is a prevailing idea that mother-of-pearl and the pearl are of the same nature; and, in consequence of this notion, numberless attempts have been made to obtain artificial pearls by means of little spheres more or less regularly cut out of mother-of-pearl.
The experiment has never been successful. A little serious examination of the subject proves that there is nothing to hope from this method. Even admitting that mother-of-pearl and pearl are the same in composition, which has not been scientifically proved, it is certain that they are not of the same constitution. Mother-of-pearl is much harder, and offers infinitely more resistance to the tools of the lapidary than the pearl. But that which is most important to be remarked is, that in the pearl the constituent layers are concentric, while in the pearls cut out of mother-of-pearl, the layers are more or less parallel.
Figs. 84 and 85 establish perfectly to the eye the complete difference presented in this respect by mother-of-pearl and the pearl.
They show, at the same time, how the light must necessarily undergo very different modifications in the two cases, and why cut mother-of-pearl can never have the same optical effects as the pearl.
Although pearl molluscs exist in all parts of the world, there are but few places where their gathering has become an instry. One of these places was formerly the Red Sea, which, in the time of the Ptolemies, proced an abundance of pearls. But the beds are probably exhausted; at any rate they are no longer worked. The two regions which for a long time have proced the most beautiful pearls are the Persian Gulf, and the Straits of Manaar which separate Ceylon from the peninsula of India.
More recently great quantities of pearl-oysters have been discovered in America, particularly in the Gulf of Mexico, upon the coasts of California, and in the vicinity of Panama.
There have been experiments made to determine the time necessary to the development of a pearl. No very certain results have been obtained; but it has been proved that at least two or three years are necessary for the formation of a pearl of any value.
Hitherto the pearl shells have been gathered by divers, who, practising the pursuit from their earliest years, end by being able to stay nearly six minutes without breathing at the bottom of the sea. The prodigious efforts which they are obliged to make, and the considerable pressure to which they are subjected, result in a number of very grave accidents. The bodies, too, of the unhappy beings who devote themselves to this frightful trade, are very quickly covered with sores; and very seldom does a pearl-diver arrive at old age.
The remarkable appliances which render it possible to stay under the water for a long time without much inconvenience have been introced into the localities where there are pearl fisheries, and will no doubt diminish wonderfully the sad consequences so long inseparable from this deadly trade.
热心网友
时间：2023-10-17 00:19
When the mussels in the sea-bed feeding, the shells open, sand, parasites and other foreign bodies falling into the occasional go, Mantle stimulated, it will secrete nacre, the layers of wrapped around foreign bodies falling into the go to make it smooth, the graal formation of pearl sac - that is, the outer layer of glowing pearls.
Therefore, the formation of pearls is round or spherical ball, the key lies in whether nacre around evenly to stimulate the accumulation of the source.
热心网友
时间：2023-10-17 00:20
how the pears are proced?
