REPRIEVE-REPRODUCTION. government, and the chief question is, By what test into two, each of these, again, dividing into two can the best approximate estimate of social value be others, and so on. This is termed reproduction by arrived at? Two different schemes for this purpose fission. The second mode of increase consists in the have been proposed by Mr J. S. Mill and Professor Lorimer respectively the former founded mainly on intelligence as indicated by instruction, and the latter on wealth and social position. The attention of political writers has also lately been directed to the question of the representation of minorities, who at present are not even allowed a hearing in representative assemblies. The most feasible scheme for this purpose is perhaps that of Mr Hare, which has the approval of Mr J. S. Mill, by which those who do not like the local candidates, are to be allowed to fill up voting papers by a selection from the names of any persons on the list of candidates, with whose general political principles they sympathise. This system, along with its other advantages, would, it is supposed, bring into parliament numerous men of able and independent thought, who, by the present system, refrain from offering themselves, as having no chance of being chosen by the majority of any existing constituency. See J. Š. Mill's Considerations on Representative Government (London, 1861); Professor Lorimer's Political Progress not necessarily Democratic (1857); and Hare's Treatise on the Election of Representatives (1860). REPRIEVE (Fr. reprendre, to take back) is the suspension of punishment for a crime, and is used chiefly in connection with capital crimes. The power of suspending all sentences at any time is vested in the crown at discretion. There are also several grounds on which the judge or a court reprieves a sentence. One is, where the judge is not satisfied with the verdict, or is doubtful of the validity of the indictment, in which case he reprieves the sentence, in order to give time for some application to the crown. Moreover, an ordinary ground of reprieve is acted on generally as a matter of course, whenever the prisoner is a pregnant woman, and pleads that fact, in which case it is considered only merciful towards the offspring to put off the execution of the sentence until after her delivery. This was the law of ancient Rome; and nothing connected with the memory of Queen Mary is more detestable than the bloody proceeding in her reign of burning a pregnant woman in Guernsey, when the child, which was born at the stake, was cast into the fire as a young heretic. When a woman pleads her pregnancy as a reason for reprieve, the practice is for the judge to empanel a jury of 12 matrons, or discreet women, to inquire into the fact, and if they bring in a verdict of 'quick with child,' execution is stayed, as a matter of course, from session to session until the delivery. Another cause of reprieve is the insanity of the prisoner, for if before execution it appear the prisoner is insane, whether the insanity supervened after the crime or not, the judge ought to reprieve him. REPRI'SAL is the retaking, from an enemy, goods which he has seized, or the capture from him of other goods, as an equivalent for the damage he has wrought.-A reprise is a ship recaptured from an enemy or pirate. If recaptured within 24 hours of the hostile seizure, she must be wholly restored to her owners; if later, she becomes the lawful prize of her recaptors. REPRISALS, LETTERS OF, the same as LETTERS OF MARQUE (q. v.). REPRODUCTION, or the propagation of organised beings in the animal kingdom, is accomplished by three different processes. The first of the three processes by which the multiplication of individuals takes place consists in the division of one organism formation of a bud at some part of the body of the animal. This bud gradually approximates in form to that of the parent from which it springs; its pedicle or stem gradually disappears; and the liberated bud ultimately assumes a perfect form, resembling in all respects the parent from which it sprung (gemmation). The third mode is far the most complicated. In it the new organism results from a series of changes occurring in an impregnated egg or ovum. For this process, distinct sexual organs, both male and female (which, however, may be associated in the same individual, although in all the higher animals they occur in distinct individuals), are required; a female organ for the production of cells termed 'germs,' and a male organ for the production of certain cells termed 'spermatozoa.' It is from the union (either within or without the body) and the mutual action of these cells-the germ and the spermatozoon-that the impregnated ovum results. The new resulting body is altogether different from either of the cells which took part in its production. This is the ordinary form of reproduction in all the higher animals, and may be termed true generation, in contradistinction to the previous forms of reproduction by multiplication. The terms Digenesis and Heterogenesis have been applied by recent physiological writers to designate the form of reproduction in which the contact of germs and spermatozoa gives rise to fecundation; while the terms Monogenesis and Homogenesis have been similarly applied to the cases in which non-sexual reproduction takes place by fission or gemmation. Fissiparous multiplication is best illustrated by a reference to the Infusoria. It may be either longitudinal, as commonly occurs in Vorticella; or trans ODUL Fig. 1.-Longitudinal Fission of Vorticella. verse, as occurs in Stentor; or indifferently longitudinal or transverse, as in Chilodon, Paramecium, &c. The joints of tape-worms multiply in this manner, and when sufficiently developed, become free. Amongst some of the Annelids, or true worms, reproduction of this kind in a somewhat modified form is also observed. This was first noticed in a Nais by the Danish naturalist Müller, by whom it was regarded as a rare and accidental occurrence. The more recent researches of De Quatrefages and Milne-Edwards have, however, shewn that the process is one of far more significance than Müller supposed. a In the genus Syllis, De Quatrefages noticed the following appearances: When one of these worms is about to reproduce itself by fission, number of rings become developed at its posterior extremity, and there is a notch or groove between the first of these rings and the part in front of it. The first ring soon becomes organised into a head provided with eyes and antennæ. The two annelids, parent and offspring, continue, however, to be united by the skin and intestine in such a manner that the latter animal lives solely upon the food swallowed by the former. During this period, each possesses independent life, for a struggle may often be observed between the two, each wishing to go its 195 REPRODUCTION. own way. 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 distention 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. Each 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 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 gemma, 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. 2 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. For a 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. 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 Cirrhopoda-the 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. 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 ovarian 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 vivi parous 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 glandular 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 seaweed at the bottom of the ocean. A brittle egg-shell would soon be destroyed by the beating of the waves; Fig. 4-The Egg of Cartila- hence the necessity for ginous Fish, opened so as to the corneous nature of shew the young animal. the envelope; and yet how is the feeble embryo to escape from such a tough and leather-like cradle? This has likewise been provided for. The egg remains permanently open at one extremity; the slightest pressure from within, therefore, separates the valvular lips of the opening, and no 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. See 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 fœtus 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. VEGETABLE PHYSIOLOGY, and FECUNDATION. REPRODUCTION IN PLANTS. See PLANT, 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. Sauria, or Lizards; 3. Loricata, or Crocodiles; and 4. Chelonia, or Tortoises; 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. With the exception of the tortoises, the reptiles in general are of an elongated form, the body being often nearly cylindrical, and usually terminating in a very long tail. In a considerable number (as the serpents and some of the lizards) no traces of limbs are apparent; in some (as certain lizards), the limbs are rudimentary; while in the remainder the limbs are fully developed, although not to the extent to which development takes place in birds or quadrupeds, as the feet rarely suffice to keep the belly from the ground. The outer covering of the body presents several well-marked varieties. In a few of the lizards, the skin is covered with regular scales, composed of a mixture of bony and horny matter, and lying over each other like those of fishes; in most REPTILES. lizards and in serpents, there are scales and plates off at intervals, the moult forming an accurate cast t, tongue and glottis; c, esophagus (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, 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 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 Fig. 2.-Anatomy of Lizard: a, a', arches of the aorta; r, right auricle; 1, left auricle; v, ventricle; ves, vena cava superior; vei, vena cava inferior; va, ventral aorta; pv, pulmonary veins; pa, pulmonary arteries; lu, lung; li, liver and hepatic vein; k, kidneys and renal vessels; vp, vena porta; s, stomach; int, intestines; an, anus. and covered over with epidermis, which is thrown 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 REPTILES. bone; and c, c the lachrymals. The lower jaw (except in the tortoises) presents the peculiarity of being composed of a number of separate pieces; there being four or five in each half-jaw in serpents, while in crocodiles and lizards each half is divided into at 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 differ-will at once perceive the striking difference. This ences than the osseous system. With the exception of certain Chelonians, 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 esophagus 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. 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, constituting the upper and lower eyelids, which can It is in their circulating and respiratory organs be drawn together by a that reptiles present the most marked character- sphincter muscle; and istics. Like birds and mammals, they breathe air, we also find a rudiment but like fishes, they are cold-blooded. The reason of a third eyelid, formed why they are unable to sustain a fixed temperature by an additional fold of above and independent of that of the surrounding membrane at the inner medium, is due partly to the arrangement of the angle, which is so comblood-vessels (see CIRCULATION), and partly to the pletely developed in structure of the lungs. The lungs are usually of crocodiles as to form a large size; but as they are not subdivided, as in mam- nictitating membrane, 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 aerating surface is but slightly increased purpose.-Carpenter's General and Comparative by sacculi developed in their cells. In serpents, the pulmonary arrangement is singular, one lung (usually the right one) being of extraordinary length, Fig. 6.-Brain of Turtle : A, olfactive ganglia; B, cerebral hemispheres; C, optic ganglia; D, cerebellum. Physiology, 3d ed. p. 495. The organ of hearing is more highly developed than in fishes or amphibia. There is no external auditory canal, the membrane |