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would be liable to be torn and bruised. Add to these incon- | into the gasteropod by placing, side by side, some intermediate veniences the fact that it would be without eyes or feelers in the forms between the more typical turbo and the river-mussel fore-part of the body to direct its course, or to take observations (Unio). In patella (the limpet) it will be seen that the gills are of what occurred, and we may judge that the benefits of travel still on both sides of the animal, as are also the muscles, though would be quite outweighed by its dangers and troubles. In the these have no longer the office of closing the shell, which, in this gasteropods, therefore, both shells are consolidated into one, and case, is consolidated into an equilateral cone. In the bonnet drawn out in an upward direction, so that, while the more deli- limpet one side of the breathing organs has been aborted, while cate organs are securely lodged, the edges of the shell's mouth in turbo both the breathing apparatus and muscles of one side are withdrawn from the ground.
are gone, and the whole animal is twisted, in its upper part, The gills are removed out of harm's way in a singular manner. I into a one-sided spire. In this case a rounded horny plate is
1., 11., III., IV. DIAGRAMS OF UNIO, PATELLA, CALYPTREA, AND TURBO, TO SHOW THE STAGES OF TRANSITION FROM THE CONCHIFER TO THE TYPICAL
GASTEROPOD. V. A SINGLE SET OF TRANSVERSE TEETH FROM (1) A SEPHORATED GASTEROPOD AND (2 AND 3) UNSEPHORATED GASTEROPODS. VI.
SHELL OF CASSIS. VII. PALUDINA. VIII. SECTION OF CERITHIUM. Ref. to Nos, in Figs.-I., II., III., IV. 1. l', lips or tentacles ; 2, mantle ; 3, shell muscles ; 4, gills ; 5, foot; 6, position of the liver ; 7,
byssus ; 8, operculum. Ví. 1, spire ; 2, suture ; 3, aperture ; 4, outer lip; 5, inner lip; 6, anterior canal for passage of the siphon ; 7, posterior canal; 8, varices. VII. 1, umbilicus. VIII, 2, columella.
Those on one side (usually the right) are brought right up and developed on the upper part of the foot, or rather tail of the placed on the animal's back, and there enclosed by a fold of the creature, and this, when the animal pulls back its head and leathery skin, and placed partially in the last or largest part of thin foot into the shell, closely closes the aperture. This the shell cavity, while those of the other side are entirely operculum, as it is called, is supposed to be the representative aborted or dispensed with. This arrangement gives a one of the horny byssus of the bivalve, being, as will be seen, sidedness to the animal, and, perhaps, is the determining cause similarly situated. of the shell being made more compact in the method peculiar to The alimentary canal commences with a mouth armed with gasteropods, namely, by being twisted into a one-sided spiral or hard parts. These are different in different creatures; but in helix, as it is technically called. The head, with its feelers, all there is a fibrous plate, bearing teeth, placed on a cushion on eyes, and ears, can be thrust out from the shell and stretched the floor of the mouth. These teeth are usually directed backwell forward, so as to gain some acquaintance with those external wards ; sometimes the plate in which they are set is very long objects which come within the line of march. In the illustration from point to back, the teeth being disposed in small cross it is shown how the conchifer may possibly have been modified rows set in parallel lines from one end of the plate to the other.
This is more especially the case in the carnivorous sea-snails, in which it is associated with a long extensible proboscis. In the land and fresh-water gasteropods belonging to the order Pulmonifera, the number in a cross direction is very great, but the lingual ribbon is much shorter. This tooth-bearing ribbon is set on a muscular pad, which can move it backward and forward, so that the little flinty teeth act as a fine file. It is curious that these teeth are composed neither of horn nor shell (CaCO.), but of silica (SiO2) or flint. They are, of course, liable to be worn away; but the ribbon is formed from behind as fast as it wears away in front; and in some species, a considerable length of it lies coiled up in a sac or pouch, which stretches away from the mouth, ready to supply the place of the continual wear and tear. A few examples of the pattern of the teeth are given in the engraving, in which only one transverse row of three different species is given. The mouth is very muscular, and has on its front and upper wall a broad horny jaw, which is flat, with a cutting edge directed downward. It is of various shapes, and is often toothed on its lower edge. In some seasnails the mouth-cavity is furnished with a long trunk, which can be unfolded from within, and used to grasp objects while they are played upon by the file-like tongue. Inside these trunks there is sometimes a toothed circle or collar of pointed fangs, which very much strengthen the hold that the creature has on its prey. It is singular that this tooth-bearing tongue is found universally, not only among the gasteropods, but also among all the higher orders of the Mollusca, so that some classifiers have associated these together as the Odontophora, or tooth-bearers. We proceed to describe the alimentary canal as it occurs in the arion, or common black slug, noticing such marked differences as occur in some other orders. A very small throat leads from the roundish buccal cavity, and this gradually dilates until it ends in a wider stomach. On the sides of the throat are situated two large glands for secreting saliva; but, though bound to the exterior of the throat by vessels, they discharge their secretion into the back part of the mouth by two ducts, which pass between the nervous collar and the attenuated portion of the throat. slugs; but in the example before us the hind part forms a kind of globular bag, and the two ducts from the liver enter just before this rounded portion. The intestine leads from the globe directly forward, so that this globular part occupies an acute angle in the course of the alimentary canal, and then, after being bent backwards and forwards two or three times, runs to a small orifice situated at the neck of the animal on the right side, close to the aperture of the breathing chamber. The stomach and intestine are closely embraced by lobes of the very large liver, which is so bound to them as to be with difficulty unravelled. In the case of the spirally-coiled and shell-bearing gasteropods, the largest masses of the liver are situated in the small end of the spiral shell. In the aplysia (the sea-hare), and some other of the gasteropods allied to it, the interior of the stomach is studded with shelly plates and spines, thus converting it into a gizzard. The breathing organs of the Gasteropoda are very various, and they have been made use of to divide the class into subclasses and orders. Thus there are four main sub-classes founded mainly on these organs. In the Opisthobranchiata the gills are branched like a tree, or gathered together in bundles and placed on the hind parts of the body behind the heart, and are either naked or only partially protected by a fold of the mantle or shell. In the Pulmonifera there is a chamber situated over the neck, and covered completely in by a thick fold of the mantle. It only receives air through an aperture, which can be closed by a muscle running round it. The walls, and especially the floor, of this chamber have large blood-vessels in them, and so constitute a kind of lung in which the blood is aêrated. In the Prosobranchiata the arrangement as to the chamber is much the same, but in the chamber lie one or two gills, usually of a comb-like or feathery form, and in these, and not in the walls of the cavity, the blood becomes oxygenated. In the carnivorous sea-snails the aperture is converted into a canal or siphon, which is often very long, and which has an anterior canal in the aperture of the shell for its accommodation, thus constituting the difference between the round-mouthed (Holostol “nnelled (Siphonostomata) shells, as shown
All the land, and most of the fresh-water snails have lungs, and belong to the sub-class Pulmonifera, while the sea snails have gills, and belong to the other sub-classes. Thus we see repeated in the Mollusca the two different kinds of breathing organs which are suited to aquatic and aerial life, which, in the vertebrates, are represented by the gills of fish and the lungs of the higher orders. From this we may infer that a gill is the necessary form of a water-breathing apparatus.
There is yet another sub-class of gasteropods called Nucleobranchiata, or Heteropoda, which have various forms of breathing organs; but these are so different in the whole of their structure from the rest that it becomes a question whether they should be classed with the gasteropods at all.
The central organ, which aids the circulation of the blood, is situated in the typical gasteropods in the partition or diaphragm, as it is called, which lies between the breathing chamber and the chamber containing the viscera. It is always at the hind part of this, and receives the blood from the gills, or central vessel of the lungs, into a chamber or auricle. From this it passes through a valve to the more muscular ventricle, and is driven by this into a vessel which almost immediately divides into two, one of which goes forward to the mouth and foot, and the other backward to the liver and all those organs which are situated in the recesses of the shell or hind cavity of the abdomen. The blood, thus distributed by vessels, is said to escape from them into the general cavity of the body, and from thence enters by wide openings to the veins which convey it to the gills or lungs. In the case of the lung-breathers it enters the diaphragm from behind, and runs in two main vessels along the margins of this organ, and then sends off smaller-vessels or sinuses towards the central vessel. In the Prosobranchiata the sexes are distinct; but in the Pulmonifera and Opisthobranchiata the sexes are united in one individual, and the organs in the former are of very complicated and peculiar structure. In the neighbourhood of the heart there is an organ which is considered to be a kidney, which eliminates the azotised products caused by the wear and tear of the vital action. This organ seems also, in some species, to have the office of introducing
The stomach is of various shapes in the water into the blood-system from without, as it has an opening
on the one side into the breathing-chamber, and on the other into the pericardium or external heart-chamber. The front part of the mantle-fold, which covers in the breathing-chamber, is thickened into a collar, and this is the instrument for secreting the shell. The shape and foldings of this edge of the mantle give rise, in the process of growth, to all those beautiful shells whose variety of colours and shape must be known to the reader. One of the characteristics of the gasteropods is the immense amount of sticky mucus they are constantly exuding, and which makes, in the land-slugs, a serious draught on their nutritive system. This is secreted by glands all over the skin, but also, in some species, by special larger glands on the back of the neck. The nervous ganglia, though they probably consist of the same elements as in the Conchifera, are gathered together so as to form a ring round the throat, situated at the narrow part just behind the buccal mass. The muscular system is almost wholly confined to the skin, except that a broad muscle arising from the lower part of the body runs to the head, and slips of this muscular sheet also go up the tentacles, so that, when in contraction, the tubular tentacle and eye-stalks are pulled into the body at the same time as the head is withdrawn. In the common snail the eye-tentacles are the longest, and are set highest on the head, while the lower pair is simply tactile. In many sea-snails there is only one pair of tentacles, the ends of which are feelers, while the eyes are set on the sides or bases of these. The eyes, themselves, are not highly organised, being little more than a nerve expanded in front of a dish of black pigment, and placed behind a transparent cornea. Ear-sacs with round ear-stones in them, are found in many Gasteropoda. The Gasteropoda are the most typical class of the Molluscathat is, they are the central group, showing fewer points a relation to the other sub-kingdoms than the other classes, an possessing a very large number of species nearly allied to on another, so that there are fewer gaps in the series. They, i. fact, occupy a similar position with regard to the Mollusca a the insects do to the Articulata, or the osseous fishes do to th
LESSONS IN ARCHITECTURE.—XVIII.
burning lava, and of course are found in an incomplete state ;
they turned on pivots, and were fastened by bolts which hung PRIVATE HOUSES.
upon chains. Bedsteads are found, made both of wood and HOMER, in his " Odyssey," informs us that the houses and even iron ; but their beds were made generally of carpets and vests, the palaces of ancient Greece were constructed of wood; and spread upon the ground. The articles of household furniture among others he particularly describes that of Ulysses, at Ithaca. and convenience found in these remarkable ruins are utensils of It is stated that the private houses of the early Romans were every kind in silver, brass, stone, and earthenware, with vases small, and that the doors were left unclosed during the principal of every size and adapted to every use; trumpets, bells, gridmeal. As wealth and luxury increased, the size of their houses irons, colanders, saucepans (some lined with silver), kettles, became so great as to accommodato, in no very extraordinary ladles, moulds for jelly or pastry, urns for keeping water hot on cases, no less than four hundred slaves under a single roof. The the principle of the modern tea-urn, horn-lanterns, spits, and, height of private houses at Rome was restricted by the Emperor in fact, every article of kitchen or other furniture used by us, Augustus to seventy feet; but the irregularity of the city be except forks; chains, bolts, scourges, dice (some said to be came so great, that in one sense its conflagration by Nero turned loaded); a complete toilet, with combs, thimbles, rings, paint, out a public good. For, being passionately fond of building, pins, earrings, pearls, etc. But for more enlarged details, we this made way for his architectural plans, and rendered Rome must refer to the work of Sir William Gell and J. P. Gandy, afterwards a regular and splendid city. Notwithstanding these entitled “Pompeiana,” in which there is given a detailed account improvements, there was a great want of conveniences in the of the excavated houses of Pompeii. private architecture of the Romans. There was a general ab The excavated towns above mentioned being small, furnished sence of chimneys and of windows; and the only light received specimens chiefly of houses inhabited by Romans of the middle in the rooms was through an aperture formed in or over the and lower classes. At Rome itself, the excavations of the villa door. In these respects, therefore, they were little removed Negroni have made us acquainted with the nature of purely from the rude cottages of the poor still to be seen in the remote Roman houses, and of the higher class. To this may be added parts of our own country. One reason for the neglect of com- the following description, by himself, of the winter residence of fort in their private dwellings was, that they were not a do- Pliny the Younger, at Laurentinum, situated at the distance of mesticated people; they lived in public and for the public, and seventeen miles from Rome, which gives us a more distinct contheir society was to be found in the Forum and public porticoes. ception of the villa of a wealthy nobleman of that city:A military people are sure to be thus circumstanced; and France, “My villa is large enough to afford all desirable accommodaat least in Paris since the first revolution, has presented a simi- tion without being extensive. The porch before it is plain, but lar spectacle to the observer. Her inhabitants live in cafés, and not mean, through which you enter a portico in the form of the in clubs or societies, but not at home.
letter D, 'which includes a small but agreeable area. This The arrangement of ancient houses greatly differed from the affords a very commodious retreat in bad weather, not only as modern in the formation of their internal courts. These were it is enclosed with windows, but particularly as it is sheltered usually constructed so that each was surrounded by apartments by an extraordinary projection of roof. From the middle of which, when lighted from within, prevented the domestic con- this portico you pass into an inward court, extremely pleasant, cerns of the family from being overlooked by any one not and thence into a handsome hall, which runs out towards the included within the walls. From a passage in Plautus, it does sea. On every side of this hall there are either folding-doors not appear that this construction always answered the purpose ; or windows equally large, by which means you have a view and in Seneca mention is made of the annoyance to which the from the front and the two sides, as it were, of three different neighbours were subject from the disorderly conduct of those seas; from the back you see the middle of the court, the portico, persons who changed night into day by indulging in the false and area; and by another view you look through the portico refinement and late hours of the age in which he lived. In into the porch, whence the prospect is terminated by the woods the Roman houses, also, there appears to have been, after the and mountains which are seen at a distance. On the left-hand Eastern fashion, a remote or inner court for the apartments of side of this hall, somewhat farther from the sea, lies a large the females, accessible only by an outer court for those of the drawing-room, and beyond that a second of a smaller size, which males, and of the servants. The information conveyed to us in has one window to the rising and another to the setting sun. the works of Vitruvius has received singular illustration and The angle which the projection forms with this drawing-room confirmation within a period less than a century, from the exca- retains and increases the warmth of the sun; and hither my vations at Pompeii, Herculaneum, and Stabia, cities which were family retreat in winter to perform their exercises. Contiguous overwhelmed by a tremendous eruption of Vesuvius in A.D. 79, to this is a room forming the segment of a circle, the windows and which contained houses built and inhabited by Romans of which are so placed as to receive the sun the whole day; in belonging to the age of Vitruvius. These excavations exhibit the walls are contained a set of cases, which hold a collection of curiously paved streets, having the tracks of carriage-wheels such authors whose works can never be read too often. Thence marked on them, and houses built of brick and rubble-work put you pass into a bed-chamber through a passage which, being together with mortar, all the materials being of very inferior boarded, and suspended over a stove which runs underneath, quality, except the interior coating of plaster, to which they tempers the heat, which it receives and conveys to all parts of appear to have been chiefly indebted for their durability. This this room. The remainder of this side of the house is approplaster was composed of lime and pounded marble, a substitute priated to the use of my slaves and freedmon; but most of the for stucco, and by its use a perfectly smooth and polished sur. apartments are neat enough to receive any of my friends. In face was obtained, nearly as hard as marble. With this kind of the opposite wing is a room ornamented in a very elegant tasto; stucco the smallest apartments at Pompeii are found to be next to which lies another room, which, though large for a lined; and this lining is painted with various and brilliant parlour, makes but a moderate dining-room. Beyond is a bedcolours, and embellished with subjects either in the centre or at chamber, together with its ante-chamber, the height of which equal distances, like panels. Painted imitations of variegated renders it cool in summer, as its being sheltered on all sides marbles, forming, perhaps, a species of scagliola, also decorate from the winds makes it warm in winter. To this apartment the walls of their houses. Few blocks of real marble are found, another of the same sort is joined by a common wall. From except in monuments and public buildings; though, in imitation thence you enter into the grand and spacious cooling-room beof the wealthy Romans, the Pompeians inserted pieces or slabs longing to the bath, from the
opposite walls of which two round of this material in their walls, and employed art to give them basins project, sufficiently large to swim in. Contiguous to this higher tints than those they possessed by nature. They also is the perfuming-room, then the sweating-room, and next to that discovered a method of veining slabs with gold; and leaves of the furnace which conveys the heat to the baths. Adjoining this metal covering the beams, walls, and even roofs of the are the two little bathing-rooms, fitted up in an elegant rather houses, were introduced in great profusion. They covered their than a costly manner. At the other end is a second turret, in floors with cement, in which small pieces of marble or coloured which
is a room that receives the rising and setting sun. Behind stones were regularly embedded in geometrical forms; and in this is a large repository, near to which is a gallery of curiositheir best rooms they used mosaic (inlaid work) with ornamented ties, and underneath is a spacious dining-room. It looks upon margins and a device in the centre. The doors of their houses, the garden and the ride which surrounds the garden. Between being formed of wood, have been reduced to charcoal by the the garden and this ride is a banqueting-room. Two apart
ments run round the back of it, the windows of which look upon kind of architecture; and there are some also in Germany and
the entrance to the villa, and into a pleasant kitchen-garden.
Italy. In the thirteenth century the Gothic style was used as
From thence an enclosed portico extends, which, by its great much in private as in monumental or public architecture. In
length, you might suppose erected for the use of the public.
It the town of St. Yrieix there is a very fine house built in this
has a range of windows on each side, but on that which looks style; and others are found at Montpazier, in the department of
towards the sea they are double the number of those next the the Dordogne.
garden. Before this portico lies a terrace, perfumed with violets. On the upper end of the terrace and portico stands a detached building in the garden, which I call my favourite; and, indeed, it is particularly so, having been erected by myself. It contains a very warm winter room, one side of which looks upon the terrace, the other has a view of the sea, and both lie exposed to the sun. Through the folding-doors you see the opposite chamber, and from the window is a prospect of the enclosed portico. On that side next the sea, and opposite the middle wall, stands a little elegant recess, which, by means of glass doors and a curtain, is either laid open to the adjoining room or separated from it. Adjoining to this is a bed-chamber, whichneither the voice of the servants, nor the murmuring of the sea, nor even the roaring of a tempest can reach. This profound tranquillity is occasioned by a passage which separates the wall of the chamber from the garden; and thus by that intervening space every noise is excluded. Annexed to this is a small stove-room, which, by opening a little window, warms the bed-chamber to the degree of heat required. Beyond this lie a chamber and ante-chamber, which enjoy the sun, though obliquely, from the time it rises till the afternoon.” The houses of princes and the palaces of emperors occupied a great extent; and besides baths, gymnasiums, and gardens, they had sometimes attached to them a basilica, a theatre, or a circus. Before the establishment of the Roman dominion in Gaul, the inhabitants, according to Vitruvius, lived in huts of a cylindrical form, covered with shingle or thatch; and in Normandy many vestiges of these are still to be found. The Romans gave to those people whom they conquered their religion, laws, and customs; and the Gauls then built their houses like those of Rome. Numerous villas or country-houses, and rural engineering residences, were to be seen in Gaul; many of these houses, as well as those built in towns, were constructed of wood placed on foundations of stone. Erected in a climate different from that of Italy, the Gallo-Roman houses, especially in the northern parts, were warmed by subterranean flues, called hypocausts. During the first ages of the monarchy, houses in Gaul or France were made of wood, exactly similar to those of the Roman period. In a description of the palace of Attila, given by the Byzantine historians, some valuable information is to be found on this subject. Some houses in stone, erected during the Roman period, are still to be found in France, with façades very similar to those of modern erection. In the towns of the south, and in the centre of France, such as Nismes, Perigueux, Metz, and Cluny, there remain some ancient specimens of this
Rural constructions, farms, and granges are found at Meslay in Touraine, and near Coulommiers. Both in the fourteenth and fifteenth centuries wooden houses were com. mon all over Europe. In the accompanying illustration is a representation of one of these, of which many specimens may be seen in England. The storeys of these houses were executed in corbel, that is, projecting one over the other—an arrangement by which the upper rooms were enlarged, but which rendered the lower storeys unwholesome, the light and the air being prevented from entering freely intotherooms they contained. This system of projecting storeys is proved to be of Oriental origin, from the cir. cumstance that it did not make its appearance in Europe until after the time of the Crusades. This system, which was proper in the East, for defending the lower part of the house from the light and heat of the sun, was absurd in climates where these were always wel. comed as delightful visitors. After the thirteenth century houses were constructed so that the gable-end of the roof fronted the street; and in the Middle Ages “to have the gable to the street" indicated the right of citizen. ship. Built without a regu. lar plan, these houses were owing to the arrangement of the windows, both dark and inconvenient within; the stairs were constructed outside, and in front of the building; and in the recesses thus formed, turrets were built, which in the fifteenth century were greatly multiplied, and added to their de coration. Wooden façades were generally more deco rated than those constructed of stone; the posts,thebeams and the panels were covered with a profusion of sculp ture in wood; the roofs wer decorated with elegant crests and graceful spires, surmounto with whimsical weather-vanes. During the Renaissance period the outward appearance of houses, as well as their intern" accommodations, were greatly improved; the façades becam more regular, and wood more rare; and when used, it * mixed with brick and stone. From this period, sculpture were spread over the fronts of houses with less profusion, an with more taste. There are many specimens of houses buil in the Renaissance style, in France, Germany, and Italy. * well as in England. The ancient towns of Rouen and More in France, furnish some of the finest examples. From that tim to the present day, private architecture has extensively in proved; the outward appearance of our houses has become le. fantastical, and the interior arrangements more convenien Since the mediaeval period the improvements in private edifies both in decoration and adaptation to the comfort of human lif have been considerable; but the progress of domestic archite ture in England will be traced in future lessons.