Charles Darwin - On The Origin Of Species, 6th Edition

On the Origin of Species, 6th Edition Darwin, Charles Published: 1872 Categorie(s): Non-Fiction, Science and Technics, Science Source: Feedbooks Note: This book is brought to you by Feedbooks http://www.feedbooks.com Strictly for personal use, not use this file for commercial purposes "But with regard to the material world, we can at least go so far as this— we can perceive that events are brought about not by insulated interpositions of Divine power, exerted in each particular case, but by the establishment of general laws."—Whewell: "Bridgewater Treatise" "The only distinct meaning of the word 'natural' is STATED, FIXED or SETTLED; since what is natural as much requires and presupposes an intelligent agent to render it so, i.e., to effect it continually or at stated times, as what is supernatural or miraculous does to effect it for once."—Butler: "Analogy of Revealed Religion" "To conclude, therefore, let no man out of a weak conceit of sobriety, or an ill-applied moderation, think or maintain, that a man can search too far or be too well studied in the book of God's word, or in the book of God's works; divinity or philosophy; but rather let men endeavour an endless progress or proficience in both."—Bacon: "Advancement of Learning" An Historical Sketch Of The Progress Of Opinion On The Origin Of Species, Previously To The Publication Of The First Edition Of This Work I will here give a brief sketch of the progress of opinion on the Origin of Species Until recently the great majority of naturalists believed that species were immutable productions, and had been separately created This view has been ably maintained by many authors Some few naturalists, on the other hand, have believed that species undergo modification, and that the existing forms of life are the descendants by true generation of pre existing forms Passing over allusions to the subject in the classical writers (Aristotle, in his "Physicae Auscultationes" (lib.2, cap.8, s.2), after remarking that rain does not fall in order to make the corn grow, any more than it falls to spoil the farmer's corn when threshed out of doors, applies the same argument to organisation; and adds (as translated by Mr Clair Grece, who first pointed out the passage to me), "So what hinders the different parts (of the body) from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident And in like manner as to other parts in which there appears to exist an adaptation to an end Wheresoever, therefore, all things together (that is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity; and whatsoever things were not thus constituted, perished and still perish." We here see the principle of natural selection shadowed forth, but how little Aristotle fully comprehended the principle, is shown by his remarks on the formation of the teeth.), the first author who in modern times has treated it in a scientific spirit was Buffon But as his opinions fluctuated greatly at different periods, and as he does not enter on the causes or means of the transformation of species, I need not here enter on details Lamarck was the first man whose conclusions on the subject excited much attention This justly celebrated naturalist first published his views in 1801; he much enlarged them in 1809 in his "Philosophie Zoologique", and subsequently, 1815, in the Introduction to his "Hist Nat des Animaux sans Vertebres" In these works he up holds the doctrine that all species, including man, are descended from other species He first did the eminent service of arousing attention to the probability of all change in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition Lamarck seems to have been chiefly led to his conclusion on the gradual change of species, by the difficulty of distinguishing species and varieties, by the almost perfect gradation of forms in certain groups, and by the analogy of domestic productions With respect to the means of modification, he attributed something to the direct action of the physical conditions of life, something to the crossing of already existing forms, and much to use and disuse, that is, to the effects of habit To this latter agency he seems to attribute all the beautiful adaptations in nature; such as the long neck of the giraffe for browsing on the branches of trees But he likewise believed in a law of progressive development, and as all the forms of life thus tend to progress, in order to account for the existence at the present day of simple productions, he maintains that such forms are now spontaneously generated (I have taken the date of the first publication of Lamarck from Isidore Geoffroy Saint- Hilaire's ("Hist Nat Generale", tom ii page 405, 1859) excellent history of opinion on this subject In this work a full account is given of Buffon's conclusions on the same subject It is curious how largely my grandfather, Dr Erasmus Darwin, anticipated the views and erroneous grounds of opinion of Lamarck in his "Zoonomia" (vol i pages 500-510), published in 1794 According to Isid Geoffroy there is no doubt that Goethe was an extreme partisan of similar views, as shown in the introduction to a work written in 1794 and 1795, but not published till long afterward; he has pointedly remarked ("Goethe als Naturforscher", von Dr Karl Meding, s 34) that the future question for naturalists will be how, for instance, cattle got their horns and not for what they are used It is rather a singular instance of the manner in which similar views arise at about the same time, that Goethe in Germany, Dr Darwin in England, and Geoffroy Saint-Hilaire (as we shall immediately see) in France, came to the same conclusion on the origin of species, in the years 1794-5.) Geoffroy Saint-Hilaire, as is stated in his "Life", written by his son, suspected, as early as 1795, that what we call species are various degenerations of the same type It was not until 1828 that he published his conviction that the same forms have not been perpetuated since the origin of all things Geoffroy seems to have relied chiefly on the conditions of life, or the "monde ambiant" as the cause of change He was cautious in drawing conclusions, and did not believe that existing species are now undergoing modification; and, as his son adds, "C'est donc un probleme a reserver entierement a l'avenir, suppose meme que l'avenir doive avoir prise sur lui." In 1813 Dr W.C Wells read before the Royal Society "An Account of a White Female, part of whose skin resembles that of a Negro"; but his paper was not published until his famous "Two Essays upon Dew and Single Vision" appeared in 1818 In this paper he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone After remarking that negroes and mulattoes enjoy an immunity from certain tropical diseases, he observes, firstly, that all animals tend to vary in some degree, and, secondly, that agriculturists improve their domesticated animals by selection; and then, he adds, but what is done in this latter case "by art, seems to be done with equal efficacy, though more slowly, by nature, in the formation of varieties of mankind, fitted for the country which they inhabit Of the accidental varieties of man, which would occur among the first few and scattered inhabitants of the middle regions of Africa, some one would be better fitted than others to bear the diseases of the country This race would consequently multiply, while the others would decrease; not only from their in ability to sustain the attacks of disease, but from their incapacity of contending with their more vigorous neighbours The colour of this vigorous race I take for granted, from what has been already said, would be dark But the same disposition to form varieties still existing, a darker and a darker race would in the course of time occur: and as the darkest would be the best fitted for the climate, this would at length become the most prevalent, if not the only race, in the particular country in which it had originated." He then extends these same views to the white inhabitants of colder climates I am indebted to Mr Rowley, of the United States, for having called my attention, through Mr Brace, to the above passage of Dr Wells' work The Hon and Rev W Herbert, afterward Dean of Manchester, in the fourth volume of the "Horticultural Transactions", 1822, and in his work on the "Amaryllidaceae" (1837, pages 19, 339), declares that "horticultural experiments have established, beyond the possibility of refutation, that botanical species are only a higher and more permanent class of varieties." He extends the same view to animals The dean believes that single species of each genus were created in an originally highly plastic condition, and that these have produced, chiefly by inter-crossing, but likewise by variation, all our existing species In 1826 Professor Grant, in the concluding paragraph in his well-known paper ("Edinburgh Philosophical Journal", vol XIV, page 283) on the Spongilla, clearly declares his belief that species are descended from other species, and that they become improved in the course of modification This same view was given in his Fifty-fifth Lecture, published in the "Lancet" in 1834 In 1831 Mr Patrick Matthew published his work on "Naval Timber and Arboriculture", in which he gives precisely the same view on the origin of species as that (presently to be alluded to) propounded by Mr Wallace and myself in the "Linnean Journal", and as that enlarged in the present volume Unfortunately the view was given by Mr Matthew very briefly in scattered passages in an appendix to a work on a different subject, so that it remained unnoticed until Mr Matthew himself drew attention to it in the "Gardeners' Chronicle", on April 7, 1860 The differences of Mr Matthew's views from mine are not of much importance: he seems to consider that the world was nearly depopulated at successive periods, and then restocked; and he gives as an alternative, that new forms may be generated "without the presence of any mold or germ of former aggregates." I am not sure that I understand some passages; but it seems that he attributes much influence to the direct action of the conditions of life He clearly saw, however, the full force of the principle of natural selection The celebrated geologist and naturalist, Von Buch, in his excellent "Description Physique des Isles Canaries" (1836, page 147), clearly expresses his belief that varieties slowly become changed into permanent species, which are no longer capable of intercrossing Rafinesque, in his "New Flora of North America", published in 1836, wrote (page 6) as follows: "All species might have been varieties once, and many varieties are gradually becoming species by assuming constant and peculiar characters;" but further on (page 18) he adds, "except the original types or ancestors of the genus." In 1843-44 Professor Haldeman ("Boston Journal of Nat Hist U States", vol iv, page 468) has ably given the arguments for and against the hypothesis of the development and modification of species: he seems to lean toward the side of change The "Vestiges of Creation" appeared in 1844 In the tenth and much improved edition (1853) the anonymous author says (page 155): "The proposition determined on after much consideration is, that the several series of animated beings, from the simplest and oldest up to the highest and most recent, are, under the providence of God, the results, FIRST, of an impulse which has been imparted to the forms of life, advancing them, in definite times, by generation, through grades of organisation terminating in the highest dicotyledons and vertebrata, these grades being few in number, and generally marked by intervals of organic character, which we find to be a practical difficulty in ascertaining affinities; SECOND, of another impulse connected with the vital forces, tending, in the course of generations, to modify organic structures in accordance with external circumstances, as food, the nature of the habitat, and the meteoric agencies, these being the 'adaptations' of the natural theologian." The author apparently believes that organisation progresses by sudden leaps, but that the effects produced by the conditions of life are gradual He argues with much force on general grounds that species are not immutable productions But I cannot see how the two supposed "impulses" account in a scientific sense for the numerous and beautiful coadaptations which we see throughout nature; I cannot see that we thus gain any insight how, for instance, a woodpecker has become adapted to its peculiar habits of life The work, from its powerful and brilliant style, though displaying in the early editions little accurate knowledge and a great want of scientific caution, immediately had a very wide circulation In my opinion it has done excellent service in this country in calling attention to the subject, in removing prejudice, and in thus preparing the ground for the reception of analogous views In 1846 the veteran geologist M.J d'Omalius d'Halloy published in an excellent though short paper ("Bulletins de l'Acad Roy Bruxelles", tom xiii, page 581) his opinion that it is more probable that new species have been produced by descent with modification than that they have been separately created: the author first promulgated this opinion in 1831 Professor Owen, in 1849 ("Nature of Limbs", page 86), wrote as follows: "The archetypal idea was manifested in the flesh under diverse such modifications, upon this planet, long prior to the existence of those animal species that actually exemplify it To what natural laws or secondary causes the orderly succession and progression of such organic phenomena may have been committed, we, as yet, are ignorant." In his address to the British Association, in 1858, he speaks (page li) of "the axiom of the continuous operation of creative power, or of the ordained becoming of living things." Further on (page xc), after referring to geographical distribution, he adds, "These phenomena shake our confidence in the conclusion that the Apteryx of New Zealand and the Red Grouse of England were distinct creations in and for those islands respectively Always, also, it may be well to bear in mind that by the word 'creation' the zoologist means 'a process he knows not what.'" He amplifies this idea by adding that when such cases as that of the Red Grouse are "enumerated by the zoologist as evidence of distinct creation of the bird in and for such islands, he chiefly expresses that he knows not how the Red Grouse came to be there, and there exclusively; signifying also, by this mode of expressing such ignorance, his belief that both the bird and the islands owed their origin to a great first Creative Cause." If we interpret these sentences given in the same address, one by the other, it appears that this eminent philosopher felt in 1858 his confidence shaken that the Apteryx and the Red Grouse first appeared in their respective homes "he knew not how," or by some process "he knew not what." This address was delivered after the papers by Mr Wallace and myself on the Origin of Species, presently to be referred to, had been read before the Linnean Society When the first edition of this work was published, I was so completely deceived, as were many others, by such expressions as "the continuous operation of creative power," that I included Professor Owen with other palaeontologists as being firmly convinced of the immutability of species; but it appears ("Anat of Vertebrates", vol iii, page 796) that this was on my part a preposterous error In the last edition of this work I inferred, and the inference still seems to me perfectly just, from a passage beginning with the words "no doubt the type- form," etc.(Ibid., vol i, page xxxv), that Professor Owen admitted that natural selection may have done something in the formation of a new species; but this it appears (Ibid., vol iii page 798) is inaccurate and without evidence I also gave some extracts from a correspondence between Professor Owen and the editor of the "London Review", from which it appeared manifest to the editor as well as to myself, that Professor Owen claimed to have promulgated the theory of natural selection before I had done so; and I expressed my surprise and satisfaction at this announcement; but as far as it is possible to understand certain recently published passages (Ibid., vol iii page 798) I have either partially or wholly again fallen into error It is consolatory to me that others find Professor Owen's controversial writings as difficult to understand and to reconcile with each other, as I As far as the mere enunciation of the principle of natural selection is concerned, it is quite immaterial whether or not Professor Owen preceded me, for both of us, as shown in this historical sketch, were long ago preceded by Dr Wells and Mr Matthews M Isidore Geoffroy Saint-Hilaire, in his lectures delivered in 1850 (of which a Resume appeared in the "Revue et Mag de Zoolog.", Jan., 1851), briefly gives his reason for believing that specific characters "sont fixes, pour chaque espece, tant qu'elle se perpetue au milieu des memes circonstances: ils se modifient, si les circonstances ambiantes viennent a changer En resume, L'OBSERVATION des animaux sauvages demontre 10 BRANCHIAL.—Pertaining to gills or branchiae CAMBRIAN SYSTEM.—A series of very ancient Palaeozoic rocks, between the Laurentian and the Silurian Until recently these were regarded as the oldest fossiliferous rocks CANIDAE.—The Dog-family, including the Dog, Wolf, Fox, Jackal, etc CARAPACE.—The shell enveloping the anterior part of the body in Crustaceans generally; applied also to the hard shelly pieces of the Cirripedes CARBONIFEROUS.—This term is applied to the great formation which includes, among other rocks, the coal-measures It belongs to the oldest, or Palaeozoic, system of formations CAUDAL.—Of or belonging to the tail CEPHALOPODS.—The highest class of the Mollusca, or softbodied animals, characterised by having the mouth surrounded by a greater or less number of fleshy arms or tentacles, which, in most living species, are furnished with sucking-cups (Examples, Cuttle-fish, Nautilus.) CETACEA.—An order of Mammalia, including the Whales, Dolphins, etc., having the form of the body fish-like, the skin naked, and only the fore limbs developed CHELONIA.—An order of Reptiles including the Turtles, Tortoises, etc CIRRIPEDES.—An order of Crustaceans including the Barnacles and Acorn- shells Their young resemble those of many other Crustaceans in form; but when mature they are always attached to other objects, either directly or by means of a stalk, and their bodies are enclosed by a calcareous shell composed of several pieces, two of which can open to give issue to a bunch of curled, jointed tentacles, which represent the limbs COCCUS.—The genus of Insects including the Cochineal In these the male is a minute, winged fly, and the female generally a motionless, berry-like mass COCOON.—A case usually of silky material, in which insects are frequently enveloped during the second or resting-stage (pupa) of their existence The term "cocoon-stage" is here used as equivalent to "pupa-stage." COELOSPERMOUS.—A term applied to those fruits of the Umbelliferae which have the seed hollowed on the inner face 557 COLEOPTERA.—Beetles, an order of Insects, having a biting mouth and the first pair of wings more or less horny, forming sheaths for the second pair, and usually meeting in a straight line down the middle of the back COLUMN.—A peculiar organ in the flowers of Orchids, in which the stamens, style and stigma (or the reproductive parts) are united COMPOSITAE or COMPOSITOUS PLANTS.—Plants in which the inflorescence consists of numerous small flowers (florets) brought together into a dense head, the base of which is enclosed by a common envelope (Examples, the Daisy, Dandelion, etc.) CONFERVAE.—The filamentous weeds of fresh water CONGLOMERATE.—A rock made up of fragments of rock or pebbles, cemented together by some other material COROLLA.—The second envelope of a flower usually composed of coloured, leaf-like organs (petals), which may be united by their edges either in the basal part or throughout CORRELATION.—The normal coincidence of one phenomenon, character, etc., with another CORYMB.—A bunch of flowers in which those springing from the lower part of the flower stalks are supported on long stalks so as to be nearly on a level with the upper ones COTYLEDONS.—The first or seed-leaves of plants CRUSTACEANS.—A class of articulated animals, having the skin of the body generally more or less hardened by the deposition of calcareous matter, breathing by means of gills (Examples, Crab, Lobster, Shrimp, etc.) CURCULIO.—The old generic term for the Beetles known as Weevils, characterised by their four-jointed feet, and by the head being produced into a sort of beak, upon the sides of which the antennae are inserted CUTANEOUS.—Of or belonging to the skin DEGRADATION.—The wearing down of land by the action of the sea or of meteoric agencies DENUDATION.—The wearing away of the surface of the land by water DEVONIAN SYSTEM or FORMATION.—A series of Palaeozoic rocks, including the Old Red Sandstone 558 DICOTYLEDONS, or DICOTYLEDONOUS PLANTS.—A class of plants characterised by having two seed-leaves, by the formation of new wood between the bark and the old wood (exogenous growth) and by the reticulation of the veins of the leaves The parts of the flowers are generally in multiples of five DIFFERENTATION.—The separation or discrimination of parts or organs which in simpler forms of life are more or less united DIMORPHIC.—Having two distinct forms.—DIMORPHISM is the condition of the appearance of the same species under two dissimilar forms DIOECIOUS.—Having the organs of the sexes upon distinct individuals DIORITE.—A peculiar form of Greenstone DORSAL.—Of or belonging to the back EDENTATA.—A peculiar order of Quadrupeds, characterised by the absence of at least the middle incisor (front) teeth in both jaws (Examples, the Sloths and Armadillos.) ELYTRA.—The hardened fore-wings of Beetles, serving as sheaths for the membranous hind-wings, which constitute the true organs of flight EMBRYO.—The young animal undergoing development within the egg or womb EMBRYOLOGY.—The study of the development of the embryo ENDEMIC.—Peculiar to a given locality ENTOMOSTRACA.—A division of the class Crustacea, having all the segments of the body usually distinct, gills attached to the feet or organs of the mouth, and the feet fringed with fine hairs They are generally of small size EOCENE.—The earliest of the three divisions of the Tertiary epoch of geologists Rocks of this age contain a small proportion of shells identical with species now living EPHEMEROUS INSECTS.—Insects allied to the May-fly FAUNA.—The totality of the animals naturally inhabiting a certain country or region, or which have lived during a given geological period FELIDAE.—The Cat-family FERAL.—Having become wild from a state of cultivation or domestication 559 FLORA.—The totality of the plants growing naturally in a country, or during a given geological period FLORETS.—Flowers imperfectly developed in some respects, and collected into a dense spike or head, as in the Grasses, the Dandelion, etc FOETAL.—Of or belonging to the foetus, or embryo in course of development FORAMINIFERA.—A class of animals of very low organisation and generally of small size, having a jelly-like body, from the surface of which delicate filaments can be given off and retracted for the prehension of external objects, and having a calcareous or sandy shell, usually divided into chambers and perforated with small apertures FOSSILIFEROUS.—Containing fossils FOSSORIAL.—Having a faculty of digging The Fossorial Hymenoptera are a group of Wasp-like Insects, which burrow in sandy soil to make nests for their young FRENUM (pl FRENA).—A small band or fold of skin FUNGI (sing FUNGUS).—A class of cellular plants, of which Mushrooms, Toadstools, and Moulds, are familiar examples FURCULA.—The forked bone formed by the union of the collar-bones in many birds, such as the common Fowl GALLINACEOUS BIRDS.—An order of birds of which the common Fowl, Turkey, and Pheasant, are well-known examples GALLUS.—The genus of birds which includes the common Fowl GANGLION.—A swelling or knot from which nerves are given off as from a centre GANOID FISHES.—Fishes covered with peculiar enamelled bony scales Most of them are extinct GERMINAL VESICLE.—A minute vesicle in the eggs of animals, from which the development of the embryo proceeds GLACIAL PERIOD.—A period of great cold and of enormous extension of ice upon the surface of the earth It is believed that glacial periods have occurred repeatedly during the geological history of the earth, but the term is generally applied to the close of the Tertiary epoch, when nearly the whole of Europe was subjected to an arctic climate 560 GLAND.—An organ which secretes or separates some peculiar product from the blood or sap of animals or plants GLOTTIS.—The opening of the windpipe into the oesophagus or gullet GNEISS.—A rock approaching granite in composition, but more or less laminated, and really produced by the alteration of a sedimentary deposit after its consolidation GRALLATORES.—The so-called wading-birds (storks, cranes, snipes, etc.), which are generally furnished with long legs, bare of feathers above the heel, and have no membranes between the toes GRANITE.—A rock consisting essentially of crystals of felspar and mica in a mass of quartz HABITAT.—The locality in which a plant or animal naturally lives HEMIPTERA.—An order or sub-order of insects, characterised by the possession of a jointed beak or rostrum, and by having the fore-wings horny in the basal portion and membranous at the extremity, where they cross each other This group includes the various species of bugs HERMAPHRODITE.—Possessing the organs of both sexes HOMOLOGY.—That relation between parts which results from their development from corresponding embryonic parts, either in different animals, as in the case of the arm of man, the fore-leg of a quadruped, and the wing of a bird; or in the same individual, as in the case of the fore and hind legs in quadrupeds, and the segments or rings and their appendages of which the body of a worm, a centipede, etc., is composed The latter is called serial homology The parts which stand in such a relation to each other are said to be homologous, and one such part or organ is called the homologue of the other In different plants the parts of the flower are homologous, and in general these parts are regarded as homologous with leaves HOMOPTERA.—An order or sub-order of insects having (like the Hemiptera) a jointed beak, but in which the fore-wings are either wholly membranous or wholly leathery, The Cicadae, frog-hoppers, and Aphides, are well-known examples HYBRID.—The offspring of the union of two distinct species 561 HYMENOPTERA.—An order of insects possessing biting jaws and usually four membranous wings in which there are a few veins Bees and wasps are familiar examples of this group HYPERTROPHIED.—Excessively developed ICHNEUMONIDAE.—A family of hymenopterous insects, the members of which lay their eggs in the bodies or eggs of other insects IMAGO.—The perfect (generally winged) reproductive state of an insect INDIGENES.—The aboriginal animal or vegetable inhabitants of a country or region INFLORESCENCE.—The mode of arrangement of the flowers of plants INFUSORIA.—A class of microscopic animalcules, so called from their having originally been observed in infusions of vegetable matters They consist of a gelatinous material enclosed in a delicate membrane, the whole or part of which is furnished with short vibrating hairs (called cilia), by means of which the animalcules swim through the water or convey the minute particles of their food to the orifice of the mouth INSECTIVOROUS.—Feeding on insects INVERTEBRATA, or INVERTEBRATE ANIMALS.—Those animals which not possess a backbone or spinal column LACUNAE.—Spaces left among the tissues in some of the lower animals and serving in place of vessels for the circulation of the fluids of the body LAMELLATED.—Furnished with lamellae or little plates LARVA (pl LARVAE).—The first condition of an insect at its issuing from the egg, when it is usually in the form of a grub, caterpillar, or maggot LARYNX.—The upper part of the windpipe opening into the gullet LAURENTIAN.—A group of greatly altered and very ancient rocks, which is greatly developed along the course of the St Laurence, whence the name It is in these that the earliest known traces of organic bodies have been found LEGUMINOSAE.—An order of plants represented by the common peas and beans, having an irregular flower in which one petal stands up like a wing, and the stamens and pistil are 562 enclosed in a sheath formed by two other petals The fruit is a pod (or legume) LEMURIDAE.—A group of four-handed animals, distinct from the monkeys and approaching the insectivorous quadrupeds in some of their characters and habits Its members have the nostrils curved or twisted, and a claw instead of a nail upon the first finger of the hind hands LEPIDOPTERA.—An order of insects, characterised by the possession of a spiral proboscis, and of four large more or less scaly wings It includes the well-known butterflies and moths LITTORAL.—Inhabiting the seashore LOESS.—A marly deposit of recent (Post-Tertiary) date, which occupies a great part of the valley of the Rhine MALACOSTRACA.—The higher division of the Crustacea, including the ordinary crabs, lobsters, shrimps, etc., together with the woodlice and sand-hoppers MAMMALIA.—The highest class of animals, including the ordinary hairy quadrupeds, the whales and man, and characterised by the production of living young which are nourished after birth by milk from the teats (MAMMAE, MAMMARY GLANDS) of the mother A striking difference in embryonic development has led to the division of this class into two great groups; in one of these, when the embryo has attained a certain stage, a vascular connection, called the PLACENTA, is formed between the embryo and the mother; in the other this is wanting, and the young are produced in a very incomplete state The former, including the greater part of the class, are called PLACENTAL MAMMALS; the latter, or APLACENTAL MAMMALS, include the Marsupials and Monotremes (ORNITHORHYNCHUS) MAMMIFEROUS.—Having mammae or teats (see MAMMALIA) MANDIBLES.—in insects, the first or uppermost pair of jaws, which are generally solid, horny, biting organs In birds the term is applied to both jaws with their horny coverings In quadrupeds the mandible is properly the lower jaw MARSUPIALS.—An order of Mammalia in which the young are born in a very incomplete state of development, and carried by the mother, while sucking, in a ventral pouch (marsupium), such as the kangaroos, opossums, etc (see MAMMALIA) 563 MAXILLAE.—in insects, the second or lower pair of jaws, which are composed of several joints and furnished with peculiar jointed appendages called palpi, or feelers MELANISM.—The opposite of albinism; an undue development of colouring material in the skin and its appendages METAMORPHIC ROCKS.—Sedimentary rocks which have undergone alteration, generally by the action of heat, subsequently to their deposition and consolidation MOLLUSCA.—One of the great divisions of the animal kingdom, including those animals which have a soft body, usually furnished with a shell, and in which the nervous ganglia, or centres, present no definite general arrangement They are generally known under the denomination of "shellfish"; the cuttle-fish, and the common snails, whelks, oysters, mussels, and cockles, may serve as examples of them MONOCOTYLEDONS, or MONOCOTYLEDONOUS PLANTS.—Plants in which the seed sends up only a single seed-leaf (or cotyledon); characterised by the absence of consecutive layers of wood in the stem (endogenous growth), by the veins of the leaves being generally straight, and by the parts of the flowers being generally in multiples of three (Examples, grasses, lilies, orchids, palms, etc.) MORAINES.—The accumulations of fragments of rock brought down by glaciers MORPHOLOGY.—The law of form or structure independent of function MYSIS-STAGE.—A stage in the development of certain crustaceans (prawns), in which they closely resemble the adults of a genus (Mysis) belonging to a slightly lower group NASCENT.—Commencing development NATATORY.—Adapted for the purpose of swimming NAUPLIUS-FORM.—The earliest stage in the development of many Crustacea, especially belonging to the lower groups In this stage the animal has a short body, with indistinct indications of a division into segments, and three pairs of fringed limbs This form of the common fresh-water CYCLOPS was described as a distinct genus under the name of NAUPLIUS NEURATION.—The arrangement of the veins or nervures in the wings of insects 564 NEUTERS.—Imperfectly developed females of certain social insects (such as ants and bees), which perform all the labours of the community Hence, they are also called WORKERS NICTITATING MEMBRANE.—A semi-transparent membrane, which can be drawn across the eye in birds and reptiles, either to moderate the effects of a strong light or to sweep particles of dust, etc., from the surface of the eye OCELLI.—The simple eyes or stemmata of insects, usually situated on the crown of the head between the great compound eyes OESOPHAGUS.—The gullet OOLITIC.—A great series of secondary rocks, so called from the texture of some of its members, which appear to be made up of a mass of small EGG-LIKE calcareous bodies OPERCULUM.—A calcareous plate employed by many Molluscae to close the aperture of their shell The OPERCULAR VALVES of Cirripedes are those which close the aperture of the shell ORBIT.—The bony cavity for the reception of the eye ORGANISM.—An organised being, whether plant or animal ORTHOSPERMOUS.—A term applied to those fruits of the Umbelliferae which have the seed straight OSCULANT.—Forms or groups apparently intermediate between and connecting other groups are said to be osculant OVA.—Eggs OVARIUM or OVARY (in plants).—The lower part of the pistil or female organ of the flower, containing the ovules or incipient seeds; by growth after the other organs of the flower have fallen, it usually becomes converted into the fruit OVIGEROUS.—Egg-bearing OVULES (of plants).—The seeds in the earliest condition PACHYDERMS.—A group of Mammalia, so called from their thick skins, and including the elephant, rhinoceros, hippopotamus, etc PALAEOZOIC.—The oldest system of fossiliferous rocks PALPI.—Jointed appendages to some of the organs of the mouth in insects and Crustacea PAPILIONACEAE.—An order of plants (see LEGUMINOSAE), The flowers of these plants are called PAPILIONACEOUS, or 565 butterfly-like, from the fancied resemblance of the expanded superior petals to the wings of a butterfly PARASITE.—An animal or plant living upon or in, and at the expense of, another organism PARTHENOGENESIS.—The production of living organisms from unimpregnated eggs or seeds PEDUNCULATED.—Supported upon a stem or stalk The pedunculated oak has its acorns borne upon a footstool PELORIA or PELORISM.—The appearance of regularity of structure in the flowers of plants which normally bear irregular flowers PELVIS.—The bony arch to which the hind limbs of vertebrate animals are articulated PETALS.—The leaves of the corolla, or second circle of organs in a flower They are usually of delicate texture and brightly coloured PHYLLODINEOUS.—Having flattened, leaf-like twigs or leafstalks instead of true leaves PIGMENT.—The colouring material produced generally in the superficial parts of animals The cells secreting it are called PIGMENT-CELLS PINNATE.—Bearing leaflets on each side of a central stalk PISTILS.—The female organs of a flower, which occupy a position in the centre of the other floral organs The pistil is generally divisible into the ovary or germen, the style and the stigma PLACENTALIA, PLACENTATA.—or PLACENTAL MAMMALS, See MAMMALIA PLANTIGRADES.—Quadrupeds which walk upon the whole sole of the foot, like the bears PLASTIC.—Readily capable of change PLEISTOCENE PERIOD.—The latest portion of the Tertiary epoch PLUMULE (in plants).—The minute bud between the seedleaves of newly-germinated plants PLUTONIC ROCKS.—Rocks supposed to have been produced by igneous action in the depths of the earth POLLEN.—The male element in flowering plants; usually a fine dust produced by the anthers, which, by contact with the stigma effects the fecundation of the seeds This impregnation 566 is brought about by means of tubes (POLLEN-TUBES) which issue from the pollen-grains adhering to the stigma, and penetrate through the tissues until they reach the ovary POLYANDROUS (flowers).—Flowers having many stamens POLYGAMOUS PLANTS.—Plants in which some flowers are unisexual and others hermaphrodite The unisexual (male and female) flowers, may be on the same or on different plants POLYMORPHIC.—Presenting many forms POLYZOARY.—The common structure formed by the cells of the Polyzoa, such as the well-known seamats PREHENSILE.—Capable of grasping PREPOTENT.—Having a superiority of power PRIMARIES.—The feathers forming the tip of the wing of a bird, and inserted upon that part which represents the hand of man PROCESSES.—Projecting portions of bones, usually for the attachment of muscles, ligaments, etc PROPOLIS.—A resinous material collected by the hivebees from the opening buds of various trees PROTEAN.—Exceedingly variable PROTOZOA.—The lowest great division of the animal kingdom These animals are composed of a gelatinous material, and show scarcely any trace of distinct organs The Infusoria, Foraminifera, and sponges, with some other forms, belong to this division PUPA (pl PUPAE).—The second stage in the development of an insect, from which it emerges in the perfect (winged) reproductive form In most insects the PUPAL STAGE is passed in perfect repose The CHRYSALIS is the pupal state of butterflies RADICLE.—The minute root of an embryo plant RAMUS.—One half of the lower jaw in the Mammalia The portion which rises to articulate with the skull is called the ASCENDING RAMUS RANGE.—The extent of country over which a plant or animal is naturally spread RANGE IN TIME expresses the distribution of a species or group through the fossiliferous beds of the earth's crust 567 RETINA.—The delicate inner coat of the eye, formed by nervous filaments spreading from the optic nerve, and serving for the perception of the impressions produced by light RETROGRESSION.—Backward development When an animal, as it approaches maturity, becomes less perfectly organised than might be expected from its early stages and known relationships, it is said to undergo a RETROGRADE DEVELOPMENT or METAMORPHOSIS RHIZOPODS.—A class of lowly organised animals (Protozoa), having a gelatinous body, the surface of which can be protruded in the form of root-like processes or filaments, which serve for locomotion and the prehension of food The most important order is that of the Foraminifera RODENTS.—The gnawing Mammalia, such as the rats, rabbits, and squirrels They are especially characterised by the possession of a single pair of chisel-like cutting teeth in each jaw, between which and the grinding teeth there is a great gap RUBUS.—The bramble genus RUDIMENTARY.—Very imperfectly developed RUMINANTS.—The group of quadrupeds which ruminate or chew the cud, such as oxen, sheep, and deer They have divided hoofs, and are destitute of front teeth in the upper jaw SACRAL.—Belonging to the sacrum, or the bone composed usually of two or more united vertebrae to which the sides of the pelvis in vertebrate animals are attached SARCODE.—The gelatinous material of which the bodies of the lowest animals (Protozoa) are composed SCUTELLAE.—The horny plates with which the feet of birds are generally more or less covered, especially in front SEDIMENTARY FORMATIONS.—Rocks deposited as sediments from water SEGMENTS.—The transverse rings of which the body of an articulate animal or annelid is composed SEPALS.—The leaves or segments of the calyx, or outermost envelope of an ordinary flower They are usually green, but sometimes brightly coloured SERRATURES.—Teeth like those of a saw SESSILE.—Not supported on a stem or footstalk 568 SILURIAN SYSTEM.—A very ancient system of fossiliferous rocks belonging to the earlier part of the Palaeozoic series SPECIALISATION.—The setting apart of a particular organ for the performance of a particular function SPINAL CORD.—The central portion of the nervous system in the Vertebrata, which descends from the brain through the arches of the vertebrae, and gives off nearly all the nerves to the various organs of the body STAMENS.—The male organs of flowering plants, standing in a circle within the petals They usually consist of a filament and an anther, the anther being the essential part in which the pollen, or fecundating dust, is formed STERNUM.—The breast-bone STIGMA.—The apical portion of the pistil in flowering plants STIPULES.—Small leafy organs placed at the base of the footstalks of the leaves in many plants STYLE.—The middle portion of the perfect pistil, which rises like a column from the ovary and supports the stigma at its summit SUBCUTANEOUS.—Situated beneath the skin SUCTORIAL.—Adapted for sucking SUTURES (in the skull).—The lines of junction of the bones of which the skull is composed TARSUS (pl TARSI).—The jointed feet of articulate animals, such as insects TELEOSTEAN FISHES.—Fishes of the kind familiar to us in the present day, having the skeleton usually completely ossified and the scales horny TENTACULA or TENTACLES.—Delicate fleshy organs of prehension or touch possessed by many of the lower animals TERTIARY.—The latest geological epoch, immediately preceding the establishment of the present order of things TRACHEA.—The windpipe or passage for the admission of air to the lungs TRIDACTYLE.—Three-fingered, or composed of three movable parts attached to a common base TRILOBITES.—A peculiar group of extinct crustaceans, somewhat resembling the woodlice in external form, and, like some of them, capable of rolling themselves up into a ball 569 Their remains are found only in the Palaeozoic rocks, and most abundantly in those of Silurian age TRIMORPHIC.—Presenting three distinct forms UMBELLIFERAE.—An order of plants in which the flowers, which contain five stamens and a pistil with two styles, are supported upon footstalks which spring from the top of the flower stem and spread out like the wires of an umbrella, so as to bring all the flowers in the same head (UMBEL) nearly to the same level (Examples, parsley and carrot.) UNGULATA.—Hoofed quadrupeds UNICELLULAR.—Consisting of a single cell VASCULAR.—Containing blood-vessels VERMIFORM.—Like a worm VERTEBRATA or VERTEBRATE ANIMALS.—The highest division of the animal kingdom, so called from the presence in most cases of a backbone composed of numerous joints or VERTEBRAE, which constitutes the centre of the skeleton and at the same time supports and protects the central parts of the nervous system WHORLS.—The circles or spiral lines in which the parts of plants are arranged upon the axis of growth WORKERS.—See neuters ZOEA-STAGE.—The earliest stage in the development of many of the higher Crustacea, so called from the name of ZOEA applied to these young animals when they were supposed to constitute a peculiar genus ZOOIDS.—In many of the lower animals (such as the Corals, Medusae, etc.) reproduction takes place in two ways, namely, by means of eggs and by a process of budding with or without separation from the parent of the product of the latter, which is often very different from that of the egg The individuality of the species is represented by the whole of the form produced between two sexual reproductions; and these forms, which are apparently individual animals, have been called ZOOIDE 570 www.feedbooks.com Food for the mind 571 ... mouth, the proportional length of the eyelids, of the orifice of the nostrils, of the tongue (not always in strict correlation with the length of beak), the size of the crop and of the upper part of. .. conviction that the same forms have not been perpetuated since the origin of all things Geoffroy seems to have relied chiefly on the conditions of life, or the "monde ambiant" as the cause of. .. by the effects of external conditions, or of habit, or of the volition of the plant itself It is, therefore, of the highest importance to gain a clear insight into the means of modification and