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REPRODUCTION.

After the lapse of a certain time, the body For some time, a portion of the food (minute infuof the offspring becomes distended with ova in some soria, entomostraca, &c.), caught and digested by cases, and with spermatozoa in others, while neither the parent, passes into the body of the offspring; of these structures is to be seen in the body of the primary animal. Complete division is at length effected, and the offspring is free. In a few days, however, their bodies burst, from the distension caused by their contents. Ova and spermatozoa are thus diffused through the water, and fecundation thus takes place. In the genus Myrianida (Autolytus, according to Grube's classification), MilneEdwards has seen no less than six new individuals (instead of a single one, as in Syllis) formed in gradual succession, one before the other, between the two terminal segments of the original body. of these new individuals, as it arrived at maturity, 1, Gemmation in Fresh-water Hydra; 2, Gemmation in and acquired the external form (in reduced dimensions) of the parents, was found to be possessed of reproductive organs, of which the original animal

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Each

Fig. 2.—Myriana, with six new individuals formed on it.

was totally devoid. The youngest and smallest

individual is the most remote from the tail.

In these instances, multiplication by division occurs as a natural process, but there are many cases in which artificial division gives rise to multiplication. Bonnet having found that a certain kind of small worm, when cut in two, reproduced a tail at the cut extremity of the cephalic half, and formed a head upon the caudal half, increased the number of sections, and finally succeeded in dividing one worm into twenty-six parts, almost all of which acquired a head and tail, and thus became distinct individuals. Corresponding results may be obtained by dividing a planaria or actinia into many segments. Reproduction by gemmation is a phenomenon of very frequent occurrence in the lower departments of the animal kingdom. In the lowest of the animal subkingdoms, the PROTOZOA, it occurs in the Rhizopoda-viz., in the Foraminifera; in the Spongia, being probably the most common form of reproduction in sponges; and in the Infusoria, as, for example, in Vorticella. In the CŒLENTERATA, it is of almost general occurrence in the classes Hydrozoa and Actinozoa; and in the MOLLUSCOIDS it occurs in Polyzoa and in Tunicata. In the accompanying figure (fig. 3), the process is shewn as it occurs in the freshwater hydra (the type of the Hydrozoa) and in Vorticella. If some hydras are kept for a few days in a glass of their native water, knot-like excrescences will be seen on their bodies. These are the buds or gemmæ, which rapidly enlarge, and each by degrees assumes the appearance of a young hydra, tentacles appearing about the mouth, just as in the original animal. |

1

Fig. 3.

Vorticella.

but when the tentacles are sufficiently developed, the young polype catches food for itself, and when it is sufficiently matured to commence an independent existence, the connecting pedicle gives way, and the young animal is free and independent.

It must be distinctly understood, that the fact of an organism reproducing itself by fission or gemmation does not by any means exclude the possibility that it may also be reproduced by fecundated ova. That this is the case, is indeed shewn in the instance of the worm Myriana, and a very large number of corroborative cases might be readily given.

In true generation, two special organs are required a female organ for producing the germ-cell or ovum, and a male organ for producing the spermcell or spermatozoon; and each form of generative apparatus consists of two parts, of which one is a formative organ-in the female, termed an ovarium, or ovary, and in the male, a testis-in which the reproductive cells are formed, and which is essential; and an efferent duct, by which the products of secretion are carried off. The male and female organs may exist in separate individuals, or they may co-exist in the same individual, giving rise to the condition known as Hermaphroditism (q. v.). The former condition is termed bisexual or diœcious, and the latter unisexual or monœcious. general description of the changes which take place in the impregnated egg, the reader is referred to the article DEVELOPMENT OF THE OVUM.

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We shall conclude with a brief notice of the mode or modes of reproduction in the different classes of animals, beginning with the lowest.

In the subkingdom PROTOZOA, reproduction takes place by all three modes, viz., by fission, gemmation, and impregnated ova; but fission is here the predominating form; and it is only in the Infusoria that there is undoubted evidence of true generation by ova and spermatozoa. It is worthy of notice, that in the Infusoria, propagation is effected in no less than four different ways-viz., by the three processes already described in this article, and by a process known as encystation.' See INFUSORIA.

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In the subkingdom CŒLENTERATA, it is found that both the Hydrozoa and the Anthozoa multiply by gemmation, by a true reproductive process, and in a few genera by fission.

In the ECHINODERMATA, fission has been observed in one class, the Holothuroidea, which, moreover, have distinct sexual organs combined in the same individual. In the other classes-the Echinoidea, Asteroidea, and Crinoidea-the sexes are separate, and generation only takes place by the union of germs or ova and spermatozoa.

In the ANNELIDA, true generation takes place, although, as has been already shewn, multiplication sometimes takes place by fission. In the lower Mollusca or Molluscoids, multiplication takes place

REPRODUCTION-REPTILES.

by gemmation and by true generation; while in the higher Mollusca, multiplication only takes place by true generation.

In the ARTICULATA-Insects, Crustaceans, &c. distinct generative organs are always present, and, excepting in one class of Crustaceans--the Cirrhopodathe sexes are distinct.

In the VERTEBRATA, we meet with the highest and most complex development of the generative function. In them, with a doubtful exception in the case of one or two genera of fishes, the sexes are always distinct.

sooner has the little shark thus extricated itself from its confinement, than the two sides close so accurately, that the fissure is imperceptible.'-R. Jones's General Outline of the Animal Kingdom, 1841, p. 534.

In the Amphibia or Batrachia, the sexes are more closely associated than in the osseous fishes, the ova being generally impregnated by the male as they escape from the abdominal cavity of the female. The mode of reproduction of one amphibian, the Surinam Toad, is remarkable and anomalous. Bee PIPA.

In the true Reptiles, the male sexual organs become more perfect, instruments being given to facilitate the impregnation of the female during that congress of the sexes which now becomes essential to fecundation.

In Birds, the generative organs present a close analogy to those of the higher reptiles. There is only a single ovary (the left) that has a bunch-like or racemous appearance; the right, with its oviduct, being always atrophied or rudimentary—a remarkable violation of symmetry, resembling that which occurs in the lungs of serpents. As prolonged uterogestation would be incompatible with flight, incubation here attains its highest perfection.

In Mammals, a new organ for the first time appears, from which that important class derives its name. In most of them (see MAMMALIA and PLACENTA), a temporary organ, termed the Placenta, is also formed, by which the foetus is nourished during uterine existence.

For further details on the subject of this article, the reader is referred to De Quatrefages's Rambles of a Naturalist, and to his Metamorphoses of Man and the Lower Animals; Dr Allen Thomson's article 'Ovum' in the Cyclopædia of Anatomy and Physiology; Dr Carpenter's Comparative Physiology ; and to Kölliker's Entwickelungsgeschichte des Menschen und der höherer Thiere.

REPRODUCTION IN PLANTS. See PLANT, VEGETABLE PHYSIOLOGY, and FECUNDATION.

The osseous and cartilaginous fishes present important, differences in their reproductive organs and in their modes of reproduction. In the osseous fishes, the essential female organ—the ovary, or roe consists of a large membranous bag, usually in two lobes, but sometimes single. When distended with ova, this organ fills the greater part of the abdominal cavity, and its lining membrane is arranged in folds, wherein the ova are formed and retained until sufficiently ripe for expulsion. They then escape into the abdominal cavity, and are expelled in almost incredible numbers through a special opening immediately behind the anus and in front of the urinary canal. As a general rule, the ova of fishes are impregnated after their expulsion; and in order that the impregnation of a sufficient number of eggs may be secured, the male secretion of fishes -the fluid containing the spermatozoa-is very abundant; the male secreting gland, which in fishes is termed the milt' or 'soft roe,' being equal in bulk to the ovary of the female. In a few instances, however, the young are hatched in the ovary, and grow to a considerable size before they are born, and in these cases-as, for example, in the viviparous blenny-impregnation must take place internally. In the cartilaginous fishes as the sharks and rays-the generative organs are of a higher type. The eggs are here always impregnated within the body of the female, the male having special organs by which true sexual congress is effected, and the ovaries form two large racemous bunches, placed on either side of the spine. The eggs are large in size, and comparatively small in number; and as each egg escapes from the ovary, it is seized by a true oviduct, which furnishes it with additional protective coverings. About the middle of this tube 'there is a thick glanзаз dular mass, destined to secrete a horny shell, in which the yelk and white of the egg become incased. The egg, when completed, has somewhat the shape of a pillow-case, with the four corners lengthened out into long tendril-like cords, whereby the egg is entangled amongst the With the exception of the tortoises, the reptiles seaweed at the bottom in general are of an elongated form, the body being of the ocean. A brittle often nearly cylindrical, and usually terminating in a egg-shell would soon very long tail. In a considerable number (as the be destroyed by the serpents and some of the lizards) no traces of limbs beating of the waves; are apparent; in some (as certain lizards), the limbs Fig. 4-The Egg of Cartila- hence the necessity for are rudimentary; while in the remainder the limbs ginous Fish, opened so as to the corneous nature of are fully developed, although not to the extent to shew the young animal. the envelope; and yet which development takes place in birds or quadhow is the feeble rupeds, as the feet rarely suffice to keep the belly embryo to escape from such a tough and leather-like from the ground. The outer covering of the body cradle? This has likewise been provided for. The presents several well-marked varieties. In a few of egg remains permanently open at one extremity; the lizards, the skin is covered with regular scales, the slightest pressure from within, therefore, composed of a mixture of bony and horny matter, separates the valvular lips of the opening, and no and lying over each other like those of fishes; in most

REPTILES (Lat. repo, I creep), constitute a class of the subkingdom Vertebrata, lying between the classes of Amphibians and Birds. They may be briefly characterised as being coldblooded, having a heart, composed of only three cavities-viz., two auricles and a single ventricle, and as breathing by lungs throughout the whole period of their existence; in which respect they differ from the Amphibians, which some zoologists associate with them, and which, in the early part of their existence, are furnished with gills for aquatic respiration. They are divided into the following orders: 1. Ophidia, or Serpents; 2. Lacertilia, or Lizards; 3. Rhynchocephalia; 4. Chelonia, or Tortoises, and 5. Crocodilia, or Crocodiles; so that, in so far as external form is concerned, the members of this class present a far greater diversity than is observed amongst the members of the other classes of vertebrates.

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REPTILES.

lizards and in serpents, there are scales and plates off at intervals, the moult forming an accurate cast

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of the body of the animal; while in the crocodiles and tortoises the scales are converted into true bony plates, which in the former are embedded in the tissue of the skin, and in the latter are united with the ribs, sternum, &c., of the internal skeleton, to form the complete bony case into which the head and limbs of the animal can be retracted.

The skeleton is completely ossified in all reptiles, and presents many points of interest to the philosophical anatomist, into which we have not space to enter. In the skeleton of the crocodiles and lizards, there is an obvious distinction of the regions of the neck, trunk, and tail. The total number of vertebræ int is often great, but it is chiefly in the caudal region that the excess occurs; there being 36 caudal vertebræ in the crocodile, and 115 in the monster lizard. In the serpents, the vertebral column is more abundantly subdivided than in any other animal; the number of vertebræ in the python being 422, of which about six-sevenths possess ribs articulated to their bodies by a ball-and-socket joint. By the motion which is thus allowed to the ribs, they become in some degree instruments of progression. In the reptiles generally (excepting the tortoises), one surface of each centrum (or body) of the vertebræ is concave and the other convex; while in the tortoises these surfaces are flat. The true skull is small, the bulk of the head being made up by the jawbones. As the sutures separating the individual bones never become obliterated, the reptilian skull

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, tongue and glottis; œ, œsophagus (partly removed, to shew heart, &c.); tr, trachea; ca, ca, carotid arteries; c, left auricle; c', right auricle; vt, ventricle of heart; vc, vena cava inferior; p,p, principal lung; p', rudimentary lung; i, stomach; int, intestines; cl, cloaca; an, anus; o, ovary; o'o', ova. developed on the surface of the corium or true skin,

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Fig. 2.-Anatomy of Lizard :

a, a', arches of the aorta; 7, right auricle; l, left auricle; v, ventricle; vcs, vena cava superior; vci, vena cava inferior; va, ventral aorta; pv, pulmonary veins; pa, pulmonary arteries; lu, lung; li. liver and hepatic vein; k, kidneys and renal vessels; up, vena portæ ; s, stomach; int, intestines; an, anus. and covered over with epidermis, which is thrown

198

Fig. 4.-Skull of Serpent.

both, the corresponding bones are indicated by the same references. 1 is the principal frontal, divided in the serpent into two parts; 2, 2 are the anterior, and 4, 4 the posterior frontals; 7 is the parietal bone, which is usually single in reptiles; 12, 12 are the mastoid bones (homologous to the mastoid process in man); 17, 17 are the intermaxillaries; 18, 18 are the maxillaries; 20, 20 are the nasals; 23 is the temporal bone (corresponding to the squamous portion of the human bone); 34, 35, 36, 37 are the dental, the articular, the angular, and the opercular portions of the inferior maxilla, or lower jaw; a is the tympanic bone, which supports the drum of the ear; b is the zygomatic or malar

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REPTILES.

bone; and c, c the lachrymals. The lower jaw (except while the other remains altogether rudimentary. in the tortoises) presents the peculiarity of being It is in the tortoises and crocodiles that the lung is composed of a number of separate pieces; there most highly developed; but if the reader will combeing four or five in each half-jaw in serpents, while pare the accompanying figure of the lug of the in crocodiles and lizards each half is divided into at turtle with a section of any mammalian lung, he least five, and generally six pieces, which are united

by suture. The four most important of these are shewn in fig. 3. The purpose of this arrangement is probably (as Dr Buckland suggested in his Bridgewater Treatise) to diminish the risk of fracture, which would otherwise attend the snapping together of their elongated jaws.

The bones of the extremities, except in the serpents, which have no limbs, correspond with those occurring in the higher vertebrata.

The mouth, except in the Chelonians, is usually provided with conical teeth, adapted rather for seizing and holding prey, than for dividing and masticating food. These teeth, like those of fishes, are successional; that is to say, new teeth are being constantly developed, whilst the older ones are regularly shed. In the crocodiles, three, or even four generations of teeth, sheathed one within the other, may often be seen in the same socket. In some instances, the teeth are attached solely to the jaws, while in others they are also attached to the pterygoid or palate bones. In Chelonians, the teeth are replaced by a horny beak, which, according to the habits of the animal, is adapted for bruising as well as cutting, and which in some species constitutes a somewhat formidable weapon.

The digestive organs present less marked differences than the osseous system. With the exception of certain families of each order, all reptiles are carnivorous, and swallow their prey whole. Hence the jaws are adapted, by their mobility and subdivision into segments, to open very widely, and the oesophagus is capable of great dilatation. The tongue is commonly free, elongated, and bifid, except in the crocodiles, in which it is immovable; whence the popular idea that these animals do not possess this organ. The stomach is sometimes scarcely larger than the œsophagus and intestines (as in serpents), while in other cases it forms a sac of considerable size. In either case, it is capable of great dilatation. A liver, pancreas, and spleen are always present, the two former glands pouring their secretions into the upper part of the intestine, which is short, wide, and not much twisted, and divided into two portions, corresponding to the small and large intestines of mammals, by a valve. It finally terminates in a wide cloaca, into which the ducts of the urinary and generative organs usually open. The anal aperture of this cloaca is transverse in serpents and lizards, and longitudinal in crocodiles and tortoises. These peculiarities in the anal aperture are accompanied by remarkable differences in the external generative organs of the male, and seem to divide the class into two great sections.

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Fig. 5.-Section of the Lung of the Turtle (reduced).

will at once perceive the striking difference. This inferiority of the respiratory apparatus of reptiles is further shewn in the absence of those means for the continuous introduction and expulsion of air which are observed in birds, and still more in mammals, and which are described in the article RESPIRATION. The cerebral portion of the nervous system in many respects resembles that of fishes, but the cerebral hemispheres are larger in proportion to the optic lobes, while the cerebellum is usually smaller. The organs of the senses are better developed than in fishes. The eye is always present in reptiles, and presents no remarkable peculiarity. We here first meet with a special arrangement for the protection of this delicate organ; for while in serpents the skin of the head passes continuously in front of the eyes, merely becoming transparent where it covers the cornea, it is doubled in most other reptiles into two folds, consti tuting the upper and lower eyelids, which can be drawn together by a sphincter muscle; and we also find a rudiment of a third eyelid, formed by an additional fold of membrane at the inner angle, which is so completely developed in crocodiles as to form a membrane,

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It is in their circulating and respiratory organs that reptiles present the most marked characteristics. Like birds and mammals, they breathe air, but like fishes, they are cold-blooded. The reason why they are unable to sustain a fixed temperature above and independent of that of the surrounding melium, is due partly to the arrangement of the blood-vessels (see CIRCULATION), and partly to the structure of the lungs. The lungs are usually of large size; but as they are not subdivided, as in mam-nictitating mals and birds, into innumerable microscopic air-cells, that can be drawn comthe real aërating surface is comparatively small. In pletely across the eye, as several orders, they are merely capacious bags, whose in birds, by a muscle specially adapted for that vascular or aërating surface is but slightly increased purpose.'-Carpenter's General and Comparative by sacculi developed in their cells. In serpents, Physiology, 3d ed. p. 495. The organ of hearing is the pulmonary arrangement is singular, one lung more highly developed than in fishes or amphibia, (usually the right one) being of extraordinary length, There is no external auditory canal, the membrane

Fig. 6.-Brain of Turtle : A, olfactive ganglia; B, cerebral hemispheres; C, optic ganglia; D, cerebellum.

REPUBLIC-REPUBLICAN.

Nine

of the tympanum being covered externally by the citizens, and every function-legislative, executive, integument of the head. The senses of taste and or judicial-not exercised directly by that body, touch are probably obtuse in most animals of this could only be exercised by parties deriving their class, and from its structure, the tongue is probably authority from it. But the extent of the franchise, rather an organ of touch than of true taste. and the mode of exercising it, varied much in these All reptiles are oviparous animals. Certain civic communities; and the most prosperous and species, however, retain their ova in a sort of long-lived was Venice, which was also the most uterine cavity, formed by a dilatation of the oviduct aristocratic of them all. In the 16th c., the Seven near its termination in the cloaca, until the develop- Provinces of the Netherlands, on their revolt from ment of the embryo is so far advanced that the Spain, adopted a republican form of government, enveloping membrane bursts previously to the as did Switzerland on becoming independent of the expulsion of the ovum, so that the young are actu- German empire. Great Britain was nominally a ally born alive-a mode of generation to which the republic for eleven years (from 1649 to 1660), and term ovo-viviparous is applied. The eggs are rela- France for the same number of years after her first tively large, and are furnished with a very large revolution (viz., from 1793 to 1805). The last yelk, for the nutrition of the young animal. They French republic lasted only five years (from 1848 are enclosed in a parchment-like shell, which con- to 1853). Switzerland is now (1871), with the exceptains very little calcareous matter. They are usually tion of the free towns of Lübeck, Bremen, and Hamdeposited in warm sandy places, well exposed to burg, and the diminutive San Marino, the only the sun, or in dunghills, in which the heat induced republic in Europe. Since 1848, the constitution of by the putrefactive process facilitates the final stage Switzerland has been of a more democratic character of embryonic development. Lizards lay from 8 to than formerly. 12 eggs, serpents from 10 to 50, tortoises from 20 The most important of modern republics is that to 26, and crocodiles from 20 to 60. In this respect of the United States of America - dating from its they differ widely from the amphibia, some of which separation from Great Britain-where pure democlay as many as 1200 eggs. The common opinion racy has been tried on a scale unknown elsewhere. that, after the expulsion of the eggs, the reptiles take Mexico has been a republic since 1824, except durno further care of their progeny, is erroneous. ing the rule of Maximilian in 1863-1867. Crocodiles and lizards have been observed to watch republics at present exist in South Americathe places which they have chosen as their nest; Peru, Chili, Paraguay, Bolivia, Colombia or New and the pythons (at all events, when in captivity) Granada, Venezuela, Ecuador, Uruguay, and the coil themselves around their eggs, and keep up a Argentine Confederation. In the republics of temperature very considerably above that of the the ancient world, the franchised classes exersurrounding medium. The sexes are always sepa- cised their power directly without any system rate; and the male generative organs, which are far of delegation or representation. The same was at more highly developed than in amphibians, present first the case in the Swiss cantons, where, howpeculiarities which, in association with the position ever, representative government has been graduof the anal aperture, have been adopted by zoologists ally introduced. Modern republics have been as a basis of classification. founded on the representative, not the direct, In relation to their habitat, it may be observed system, which can hardly exist except in a comthat most of the tortoises and certain serpents are munity that is very small and concentrated as to essentially aquatic animals (some inhabiting fresh, space. Switzerland and the United States of and some salt water), which rarely seek the land ex-America are federal republics, consisting of a cept for the purpose of laying their eggs. Serpents, number of separate states bound together by a however, as a general rule, affect moist places in the treaty, so as to present to the external world the neighbourhood of water, although some are inhabit- appearance of one state with a central government, ants of dry sandy deserts. Lizards for the most part which has the power of enacting laws and issuing frequent the sandy districts of hot and tropical orders which are directly binding on the individual regions, and either burrow in the ground or live in citizens. holes in trees, walls, &c. Reptiles generally predominate in the warmer regions of the globe, in which alone the largest kinds are to be found. In the northern countries, comparatively few species are found, and these pass a great portion of the year in a state of Hybernation (q. v.) or torpidity. Carpenter puts down 2000 as about the probable number of existing species of reptiles. Schinz states that in Europe there are 7 tortoises, 33 serpents, and 35 lizards. The most complete treatise on the natural history of reptiles is that of M.M. Dumeril and Bibron, in 9 volumes; it is entitled Erpétologie Générale, ou Hist. Nat. Com-rights of the people; and finally secured those plète des Reptiles (Paris, 1834—1854).

REPUBLICAN, a party name in American politics, which has had at different times different significations. At the adoption of the Federal Constitution in 1787, and while its ratification by the several states was under discussion, the country

Dr was
was divided into two parties-the Federalists,

headed by Washington and the elder Adams; and
the Anti-federalists (who afterwards took the name
of Republicans), under the lead of Jefferson and
Madison. The Federalists were in favour of a
strong centralised government; the Republicans
advocated the sovereignty of the States and the

amendments and additions to the Constitution REPUBLIC (Lat. res publica, the public good), a which were intended to guarantee state rights, and political community in which the sovereign power which declared that all powers not expressly granted is lodged, not in a hereditary chief, but either in to Congress by the Constitution, are retained by the certain privileged members of the community, or in States or the people. During the French Revolution the whole community. According to the constitu- and the wars which succeeded it, the Federal party tion of the governing body, a republic may there- sympathised with England, while the Republicans fore vary from the most exclusive oligarchy to a favoured the French; and being in power, under pure democracy. The several republics of Greece, the presidency of Mr Madison, declared war against and that of Rome were, at the outset at least, aris- England in 1812, a measure which the Federalists tocratic communities. The medieval republics violently opposed, going so far in the Hartford of Venice, Genoa, and the other Italian towns were Convention as to threaten a dissolution of the union. also more or less aristocratic. The sovereign During the political excitements of this period, power was held to be vested in the franchised when the excesses of the French revolution had

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