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GASES.

As a point of historical interest, we may mention that many years before the publication of Faraday's earliest researches on this subject, sulphurous acid gas had been liquefied by Monge and Clouet, ammonia by Guyton Morveau, and arseniuretted hydrogen by Štromeyer, by the simple application of cold, without any increased pressure.

The expansion and contraction of gases by changes of temperature is treated of under HEAT.

The process of intermixture in gases, and the movements of these substances generally, have been very carefully studied by Faraday, Döbereiner, Mitchell, Bunsen, and especially Graham. These movements are usually considered under four heads, viz.: 1. Diffusion, or the intermixture of one gas with another; 2. Effusion, or the escape of a gas through a minute aperture in a thin plate into a vacuum; 3. Transpiration, or the passage of different gases through long capillary tubes into a rarefied atmosphere; 4. Osmosis, or the passage of gases through diaphragms.

In the article Diffusion (q. v.), the general principles of this kind of movement in gases are sufficiently explained, and we shall merely make one or two supplementary remarks, chiefly with the view of rendering the following table more intel

ligible. Graham's experiments with the simple diffusion-tube shew (see Graham's Memoirs in the Transactions of the Royal Societies of London and Edinburgh, or Miller's Chemical Physics) that the diffusiveness or diffusion volume of a gas is in the inverse ratio of the square root of its density; consequently, the squares of the times of equal diffusion of the different gases are in the ratio of their specific gravities. Thus, the density of air being taken as the standard of comparison at 1, the square root of that density is 1, and its diffusion volume is also 1; the density of hydrogen is 0-0692, the square root of that density is 0-2632, and its diffusion volume is 3, or 37994; or, as actual experiment shews, 383-that is to say, if hydrogen and common air be placed under circumstances favouring their mutual diffusion, 3.83 volumes of hydrogen will change place with 100 of air. The following table gives: 1. The density; 2. The square root of the density; 3. The calculated, and 4. The observed velocity of diffusion or diffusiveness of several important gases; the numbers in the last column, headed 'Rate of Effusion,' being the results obtained by experiment upon the rapidity with which the different gases escape into a vacuum through a minute aperture about of an inch in diameter.

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"The process of diffusion,' says Professor Miller, | 1.369; of sulphuretted hydrogen, 1-614; of ammonia, 'is one which is continually performing an important 1935; of olefiant gas, 1980; and of hydrogen, 2-288. part in the atmosphere around us. Accumulations In the passage of gases through diaphragms, the gases which are unfit for the support of animal law of the diffusion of gases is more or less disturbed and vegetable life are by its means silently and or modified according to the force of adhesion in speedily dispersed, and this process thereby contri- the material of which the diaphragm is composed; butes largely to maintain that uniformity in the the disturbance being greatest in the case of composition of the aerial ocean which is so essential soluble gases and a moist thin diaphragm, such as to the comfort and health of the animal creation. a bladder or a rabbit's stomach. For details on Respiration itself, but for the process of diffusion, this subject we must, however, refer to the article would fail of its appointed end, in rapidly renewing OSMOSIS. to the lungs a fresh supply of air, in place of that which has been rendered unfit for the support of life by the chemical changes which it has undergone.'

A reference to the last two columns of the above table shews that, within the limits of experimental errors, the rate of effusion of each gas coincides with its rate of diffusion.

Graham's experiments shew that the velocity of transpiration (the term which that chemist applied to the passage of gas through long capillary tubes) is entirely independent of the rate of diffusion, or of any other known property. It varies with the chemical nature of the gas, and is most probably 'the resultant of a kind of elasticity depending upon the absolute quantity of heat, latent as well as sensible, which different gases contain under the same volume; and therefore will be found to be connected more immediately with the specific heat than with any other property of gases.' Oxygen is found to have the lowest rate of transpiration. Taking its transpiration velocity at 1, that of air is 1.1074; of nitrogen, 1·141; of carbonic acid,

All gases are more or less soluble in water and other liquids. Some gases, as, for example, hydrochloric acid and ammonia, are absorbed by water very rapidly, and to a great extent, the liquid taking up 400 or 600 times its bulk of the gas; in other cases, as carbonic acid, water takes up its own volume of the gas; whilst in the case of nitrogen, oxygen, and hydrogen, it does not take up more than from

to of its bulk. 'As the elasticity of the gas,' says Professor Miller, 'is the power which is here opposed to adhesion, and which at length limits the quantity dissolved, it is found that the solubility of each gas is greater, the lower the temperature, and the greater the pressure exerted upon the surface of the liquid. Dr Henry found that at any given temperature the volume of any gas which was absorbed was uniform, whatever might be the pressure; consequently, that the weight of any given gas absorbed by a given volume of any bquid at a fixed temperature, increased directly with the pro sure. If the pressure be uniform, the quantity of any given gas absorbed by a given liquad is also uniform for each temperature; and the numerical

GASES.

expression of the solubility of each gas in such liquids, is termed its coefficient of absorption or of solubility, at the particular temperature and pressure, the volume of the gas absorbed being in all cases calculated for 32 F., under a pressure of 29-92 inches of mercury. Thus, 1 volume of water at 32, and under a pressure of 29.92 inches of the barometer, dissolves 0-04114 of its volume of oxygen; and this fraction represents the coefficient of absorption of oxygen at that temperature and pressure. Similarly, the coefficient of absorption of common air is 002471. In consequence of this solubility of the air, all water contains a certain small proportion of it in solution; and if placed in a vessel under the air-pump, so as to remove the atmospheric pressure from its surface, the dissolved gases rise in minute

bubbles. Small as is the quantity of oxygen thus taken up by water from the atmosphere, it is the means of maintaining the life of all aquatic animals. If the air be expelled from water by boiling, and it be covered with a layer of oil, to prevent it from again absorbing air, fish or any aquatic animals placed in such water quickly perish. Even the life of the superior animals is dependent upon the solubility of oxygen in the fluid which moistens the air-tubes of the lungs, in consequence of which this gas is absorbed into the mass of the blood, and circulates through the pulmonary vessels.'

The following table, drawn up from the researches of Bunsen and Carius, shews the solubility of some of the most important gases, both in water and alcohol:

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All these gases, with the exception of hydrochloric acid, may be expelled from the water by longcontinued boiling.

Gases are not absorbed by all liquids in the same order; for example, naphtha absorbs most olefiant gas, oil of lavender most protoxide of nitrogen, olive oil most carbonic acid, and solution of chloride of potassium most carbonic oxide.

If a mixture of two or more gases be agitated with water, or probably any other liquid, a portion of each gas will be absorbed, and the amount of each so absorbed or dissolved will be proportional to the relative volume of each gas multiplied with its coefficient of solubility at the observed temperature and pressure. As all ordinary liquids exert a greater or less solvent action on gases, a gas that we wish to examine quantitatively should be collected over mercury.

and especially charcoal, exert on gases. Owing to this property of charcoal-especially freshly burned vegetable charcoal-various gases may be separated from their watery solution by filtration of the latter through it; for example, sulphuretted hydrogen may be removed from water so completely that it cannot be detected either by its well-known odour or by the ordinary tests. Saussure found that 1 volume of freshly burned box-wood charcoal absorbed 90 volumes of ammonia, 85 of hydrochloric acid, 65 of sulphurous acid, 55 of sulphuretted hydrogen, 40 of protoxide of nitrogen, 35 of carbonic acid, 35 of bi-carburetted hydrogen, 94 of carbonic oxide, 92 of oxygen, 75 of nitrogen, 50 of carburetted hydrogen, and 17 of hydrogen. These results follow an order very nearly the same as that of the solubility of the gases in water.

Stenhouse has investigated the differences in the absorbent power of different kinds of charcoal; the following are his most important results: 0.5 of a gramme of each kind of charcoal being employed, and the numbers in the table indicating in cubic centimetres the quantity of absorbed gas.

Gas Used

Kind of Charcoal employed.

The adhesion of gases to solids next requires notice. Illustrations of this phenomenon perpetually occur. Thus, wood and other solid substances immersed in water or other liquids appear covered with air-bubbles. It is this adhesion of air to the surface of glass tubes which causes the difficulty of obtaining barometers and thermometers completely free from air. It is in consequence of the adhesion of air to their surfaces that many small insects are enabled to skim lightly over the surface of water which does not wet them. A simple method of illustrating this phenomenon is by gently dusting iron filings over the surface of a vessel of water; if we proceed carefully, a considerable mass of the iron may accumulate upon the surface; till, at last, it falls in large flakes, carrying down with it numerous bubbles of air. As the particles of iron are nearly So rapid is this action of charcoal, that Stenhouse ight times as heavy as water, it was only the has proposed to use a respirator filled with it to adherent air that enabled them to float upon the protect the mouth and nostrils in an infected atmo. surface. Closely allied to this adhesion is the remark-sphere; and the employment of trays of powdered sble property of condensation which porous bodies, wood-charcoal in dissecting-rooms, in the wards of

Ammonia,.
Hydrochloric Acid,
Sulphurous Acid,
Sulphuretted Hydrogen,
Carbonic Acid,
Oxygen,

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Wood.

Peat. Animal

98.5

96.0

43.5

45.0

60'0

32.5

27.5

17.5

30.0

28.5

9.0

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GASKELL-GASSENDL

Lospitals, and in situations where putrescent animal matter is present, is found to act very beneficially in purifying the air by absorbing the offensive gases. Its use in reference to the filtration of water has been already alluded to.

The determination of the exact specific gravity of the different gases is of great importance in calculating the proportions of the different ingredients of compounds into which they enter; and the whole series of numbers expressing the chemical equivalents or atomic weights of bodies depend upon the accuracy of the determination of the specific gravity of hydrogen and oxygen.

The following table gives the specific gravity and the weight of 100 cubic inches of some of the most important gases at a barometric pressure of 30 inches, and at a temperature of 60°, together with

the name of the observer:

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The methods employed for determining the specific gravity of a gas, both by direct observation and by calculation, will be noticed in the article SPECIFIC GRAVITY.

As to the chemical properties of gases, most of the different gases, when pure, can be readily distinguished by some well-marked physical or chemical property. Some are distinguished by their colour, others by their peculiar odour; but several of the most important ones-viz., oxygen, nitrogen, hydrogen, carbonic acid, carbonic oxide, light carburetted hydrogen, olefiant gas, and protoxide of nitrogen-require other means for their discrimination. The distinctive characters of the most important gases are noticed in the articles OXYGEN, HYDROGEN, CHLORINE, &c., and the outlines of the general method of analysing a gaseous mixture are given in a separate article. For further details on the physical and chemical characters of the gases, we must refer to Miller's Elements of Chemistry, and especially to the volume on Chemical Physics, from which we have borrowed freely; to Kekule's Lehrbuch der Organischen Chemie, 1859; and to Roscoe's translation of Bunsen's Gasometry.

GASKELL, MRS ELIZABETH C., an English authoress, was born about the year 1820, and is the wife of a Unitarian clergyman in Manchester. Her maiden name was Stevenson. Her novels, of which Mary Barton (1848) and Ruth (1853) are perhaps the best examples, are chiefly descriptive of the habits, thoughts, privations, and struggles of the industrial poor, as these are to be found in such a social beehive as the city in which the authoress resides. Some of her characters are drawn with remarkable dramatic power, and many of her descriptive passages are very graphic. Among her other works may be mentioned The Moorland Cottage (1850), a Christmas story; North and South (1855); Cranford; and Lizzie Leigh—the last three of which originally appeared in Household Words. Mrs G. has edited a very interesting life of Charlotte Bronte (q. v.),

1857. Her last work, Round the Sofa, appeared in 1859. GASOMETER. See GAS.

GASPÉ, the most easterly district of Lower Canada, consisting of the counties of Gaspe and Bonaventure, is chiefly a peninsula projecting into the Gulf of St Lawrence, between the estuary of the same name on the north and the Bay of Chaleur on the south. It stretches in N. lat. between 48° and 49° 20′, and in W. long. between 64° 15′ and 67° 56', containing 7500 square miles, and about 12,000 inhabitants, the greater number being of French descent. Cod and whale fisheries form the staple business of the country. The district is terminated towards the east by a cape of its own name, and this headland is the northern extremity of a bay also of the same name, which presents a safe and capacious harbour.

GASSENDI, or GASSEND, PIERRE, an eminent French philosopher and mathematician, was born 22d January 1592, at Champtercier, a little village of Provence, in the department of the Lower Alps. His unusual powers of mind shewed themselves at an early age; and in 1616 he became professor of theology at Aix. About this time, he drew upon himself the regards of Pieresc, whom Bayle calls the procureur-general of literature, and of Joseph Gautier, prior of La Valette, a distinguished mathematician, both of whom liberally gave him the benefit of their instructions and advice. With the first, he studied anatomy; from the second, he derived his taste for astronomical observations. After six years' study, he and undertook to maintain certain theses against became disgusted with the scholastic philosophy, the Aristotelians. His polemic appeared at Grenoble in 1624, and was entitled Exercitationes paradoxica adversus Aristoteleos. It was accompanied by an expression of his belief in the church, for whose shed the last drop of his blood.' He drew a dishonour and glory he declared himself ready to tinction for the first time between the church and must stand or fall by the latter. G. now visited the scholastic philosophy, denying that the former Paris, where he made several influential friends. In the same year in which he published his Exerci tationes, he was appointed prevôt of the cathedral at Digne, an office which enabled him to pursue without distraction his astronomical and philo sophical studies. In 1628 he travelled in Holland, and got involved in a controversy with Robert Fludd, an English mystic, relative to the Mosaic cosmogony, in which he is admitted to have had greatly the advantage of his incoherent opponent. At the recommendation of the Archbishop of Lyon, a brother of Cardinal Richelieu, G. was appointed professor of mathematics in the College Royal de France, at Paris, where he died, 14th October 1655. As a philosopher, G. maintained, with great learning and ingenuity, most, though not all, of the doctrines of Epicurus, these being most easily brought into harmony with his own scientific acquirements and modes of thought. His philosophy was in such repute, that the savans of that time were divided into Cartesians and Gassendists. The two chiefs themselves always entertained the highest respect for each other, and were at one time on the friendliest terms. The agreeableness of their intercourse, however, was for a while interrupted by the publication of a work of G.'s, entitled Dubitationes ad Meditationes Cartesi, in which he expressed himself dissatisfied with the tendencies of the new system of philosophy introduced by Descartes, for G. was averse to novelty in the sphere of mental speculation, although he

GASSNER-GASTEROPODA.

warmly espoused the side of progress in physical science, and made himself many enemies among his bigoted ecclesiastical brethren for the love he bore it. He ranked Kepler and Galileo among his friends, and was himself the instructor of Molière. His principal work is entitled De vita, moribus et doctrina Epicuri (Lyon, 1647), to which the Syntagma Philosophie Epicurea (1649) belongs. It contains complete view of the system of Epicurus. His Institutio Astronomica (1645) is a clear and connected representation of the state of the science in his own day; in his Tychonis Brahai, Nicolai Copernici, Georgii Peur bachii et Joannis Regeomon-It contains a considerable quantity of creasote, tani Astronomorum Celebrium Vitae (Par. 1654), he not only gives a masterly account of the lives of these men, but likewise a complete history of astronomy down to his own time. G. was pronounced by Bayle the greatest philosopher among scholars, and the greatest scholar among philosophers. His works were collected and published by Montmor and Sorbière (Lyon, 6 vols. 1658).

GASSNER, JOHANN JOSEPH, a man who made

a

noise as an exorcist in the 18th c., was born 28th August 1727, at Bratz, near Pludenz, in the Tyrol, and became Catholic priest at Klösterle, in the diocese of Coire. While in that office, the accounts of demoniacs in the New Testament, combined with the writings of celebrated magicians, brought him to the conviction that most diseases are attributable to evil spirits, whose power can be destroyed only by conjuration and prayer. He began to carry out his conviction by practising on some of his parishioners, and succeeded so far as to attract notice at least. The Bishop of Constance called him to his residence, but having come very soon to the conviction that he was a charlatan, advised him to return to his parsonage. G. betook himself, however, to other prelates of the empire, some of whom believed that his cures were miraculous. In 1774, he even received a call from the bishop at Ratisbon, to Ellwangen, where, by the mere word of command, Cesset (Give over), he cured persons who pretended to be lame or blind, but especially those afflicted with convulsions and epilepsy, who were all supposed to be possessed by the devil. Although an official person kept a continued record of his cures, in which the most extraordinary things were testified, yet it was found only too soon that G. very often made persons in health play the part of

those in sickness, and that his cures of real sufferers

were successful only so long as their imagination remained heated by the persuasions of the conjuror. Intelligent men raised their voice against him, and he lost all respect before his death. He died, March 1779, in possession of the wealthy deanery of Benndorf.

GAS-TAR, or COAL-TAR, a thick, black, opaque liquid, which comes over and condenses in the pipes when gas is distilled from coal. It is slightly heavier than water, and has a strong, disagreeable odour. Coal-tar is a mixture of many distinct liquid and solid substances, and the separation of the more useful of these constitutes an important branch of manufacturing chemistry. The tar is first distilled in large malleable iron stills, when water and crude naphtha first come over; and afterwards, when the temperature rises, heavy, fetid-smelling oil, called dead-oil, which inks in water. There remains in the still a large residue of pitch, which is again distilled in brick ovens, giving off an oil called coke-oil, and leaving a large quantity of pitch-coke. The crude naphtha purified by sulphuric acid and quicklime, and re-distilled, when it is nearly as colourless as water. This, then, forms the refined coal-tar naphtha of

commerce. It is largely used for burning in lamps, as a solvent for india-rubber and guttapercha, to preserve animal substances from moth, and it is also burned to produce a fine carbon for the manufacture of printing-ink. It is from the lighter portion of naphtha, called benzole, that the beautiful mauve and magenta colours are manufactured. See BENZOLE and DYE-STUFFS. Benzole is likewise used for removing stains of fat or oil from cloth. The dead-oil or pitch-oil is sometimes used, in its crude state, as a cheap material for affording light in lamps burned in the open air. and forms the best preservative for wood in damp situations. The coke-oil is not of much commercial importance, but it can be burned in lamps, and this, with the dead-oil, when consumed in a confined atmosphere, gives a smoky flame, the soot from which constitutes lampblack. The pitch-coke is valuable as a fuel for melting iron, being free from impurities. Pitch itself is used for making asphalt pavement, and also for roofing-felt.

From the last portion of the distillation of the crude naphtha, and the first of the dead-oil, a beautiful white crystalline solid, called naphthaline, is obtained. It has been long known without being to be employed for the manufacture of colours, in applied to any useful purpose, but is now beginning a similar way to the benzole. The dead-oil also termed paranaphthaline, which is a mere chemical contains considerable quantities of a yellow solid curiosity.

The creasote is extracted from the dead-oil by stirring it with soda, in which the creasote dissolves. When this soda solution is boiled for some hours, and then has an acid added to it, the creasote separates as an oil on the surface of the fluid, and, when distilled, is nearly pure. This treatment requires to be repeated several times to get it quite pure, and to keep its colour. Most of the creasote used by druggists is made from coal-tar. The creasote from wood is a similar but quite distinct body.

and the crude naphtha several volatile basic oils Sulphuric acid extracts both from the dead-oil besides benzole-namely, toluole, xylole, cumole, and cymole, which are almost unknown in the arts, although they may yet come to be of great service. Among them is aniline, but not in sufficient quantity to pay for its extraction. There also occurs a curious body named pyrrol, the vapour of which gives to fir-wood, dipped in muriatic acid, have been made from these basic oils, but only a splendid violet colour. Beautiful blue colours by elaborate and expensive processes.

GASTERO'PODA (Gr. belly-footed), or GASTROPODS, a class of molluscs, inferior in organisation to cephalopods, but far superior to almost all other molluscs, and containing a multitude of species, the greater number of which are marine, but some are inhabitants of fresh water, and some are terrestrial. Snails, whelks, periwinkles, limpets, cowries, and the greater number of molluscs with univalve shells belong to this class, and univalve molluscs constitute the greater part of it; but it contains also some molluscs with multivalve shells, as chitons, and some, as slugs, which have either only a rudimental internal shell, or no shell at all. Some aquatic kinds are destitute of shell in the adult state, but they are protected by a rudimentary shell on first issuing from the egg. No known gastropod has a bivalve shell, unless the operculum, which closes the mouth of the shell in many species, be regarded as a second valve.

Gastropods have a head, more or less fully developed, in which is situated the mouth, and

GASTEROPODA.

which generally carries fleshy, retractile tentacula, varying from two to six in number. The tentaeula do not encircle the mouth; they seem to be

Fig. shewing the soft parts of a Gasteropod (Dolium Galea):

a, head; d, d, foot.

special and exquisitely sensitive organs of touch, a sense which the general surface of the body does not seem to possess in a high degree; and in some G., as snails, they carry the eyes at their

Anatomy of the Whelk (copied from Jones' Gen. Struc. of An. Kingd.):

b, vein of proboscis and its branches; c, c, nervous branches proceeding from the brain to the extremity of the proboscis; d, brain, situated above the esophagus or gullet; e, nervous branches connecting the brain with the great ganglion or nervous mass beneath the esophagus: f, tentacula; 9, penis; h, liver; i, a large nervous mass beneath the esophagus; k, l, ganglia; m, one of the two principal trunks of the aorta, supplying the foot and anterior part of the body; n, o, nervous branches connecting ganglia; p, orifice of respiratory cavity; q, branchial vein; rs, heart (r, ventricle; 8, auricle); t, one of the two principal trunks of the aorta, winding among the mass of viscera contained in the shell, and distributing its ramifications to them; u, branchial fringes, or gills; we, posterior part of the body, or mass of viscera contained in the shell; x, roof of respiratory

cavity thrown back.

tips, but in others the eyes-always small-are situated elsewhere on the head, and a few are destitute of eyes. They are believed to possess the

senses of taste and smell, and at least some of them that also of hearing, as they not only have a nervous centre analogous to the acoustic division of the brain in vertebrate animals, but a little sac on each side, apparently an organ of this sense. Their nervous system is more complex and concentrated than that of the headless (acephalous) molluscs; the principal nervous masses surround the gullet. In the highest G., such as snails, there are only two principal nervous masses, one of which, supplying the nerves connected with sensation, is called the brain. The blood of G. is often opalescent, with a few colourless corpuscles. The heart is always systemic only, and in almost all consists of one auricle and one ventricle, although a few G. have two auricles, one for each set of gills. Near the commencement of the aorta, there is often a contractile muscular swelling (bulbus arteriosus), as in fishes. Respiration takes place generally by gills, which are very variously situated, sometimes externally, sometimes in a special cavity, and exhibit an equally great variety of form and structure; but some G., as snails and slugs, have, instead of gills, a pulmonary sac or cavity, lined with a vascular net-work, these being either inhabitants of the land, or, if of the water, obliged to come occasionally to the surface for the purpose of breathing. A few of the lowest G., doubtfully placed in this class, are destitute of distinct respiratory organs. The digestive apparatus also exhibits much diversity. Some of the G. feed on vegetable, some on animal substances, and some of them on animals which they themselves kill. Thus, whilst snails eat leaves and other soft parts of vegetables, whelks (Buccinum) prey on other molluscs, and are provided with a remarkable apparatus at the end of a proboscis into which the mouth is elongated, for filing a hole -as nice as could be made by the drill of a mechanic-through the hardest shell. The mouth of the snail is, in like manner, admirably adapted to the cutting of leaves or similar substances by the action of the lips against a sharp horny plate. Other G. have the mouth furnished with two cutting blades, wrought by powerful muscles. The tongue of some is covered with minute recurved hooks, to prevent the possibility of anything escaping from the mouth; and the stomach of some is a muscular gizzard, provided with cartilaginous or sometimes calcareous projections, or stomachic teeth, to aid in the comminution of the food. The intestine is generally bent back, so that the anus is not far from the head. The liver is large, as are also the salivary glands of many gastropods. Very great diversities are found in the reproductive system. In some G., the sexes are distinct (G. DIECIA); others are hermaphrodite (G. MONECIA); and whilst self-impregnation takes place in some of these, others as snails-mutually impregnate each other by copulation. In general, the reproductive organs are very largely developed, and are of complex and remarkable structure. The G. are in general oviparous; a few are ovoviviparous. The young of aquatic G. at first swim about actively by means of ciliated fins attached to the head. G. are generally unsymmetrical, one side of the body being developed without the other, some of the principal organs of which-the gills and nerves-are atrophied; and thus the shell with which most of them are covered becomes, in the greater number, spiral, the spire turning towards the unatrophied side, which is generally the right side, although in some (reversed or sinistrorsal shells) it is the left. The head and the organ of locomotion are capable of being with drawn into the last whorl of the shell, and in aquatic species generally, the mouth of the shell can be closed by an operculum (q. v.), exactly fitting

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