They are usually green, but sometimes brightly coloured.
SERRATURES .-- Teeth like those of a saw.
SESSILE .-- Not supported on a stem or footstalk.
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.

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.
INDEX.
Aberrant groups Abyssinia, plants of Acclimatisation Adoxa Affinities of extinct species -- of organic beings Agassiz on Amblyopsis -- on groups of species suddenly appearing -- on prophetic forms -- on embryological succession -- on the Glacial period -- on embryological characters -- on the latest tertiary forms -- on parallelism of embryological development and geological succession -- Alex., on pedicellariae Algae of New Zealand Alligators, males, fighting Alternate generations Amblyopsis, blind fish America, North, productions allied to those of Europe -- boulders and glaciers of -- South, no modern formations on west coast Ammonites, sudden extinction of Anagallis, sterility of Analogy of variations Andaman Islands inhabited by a toad Ancylus Animals, not domesticated from being variable -- domestic; descended from several stocks -- acclimatisation of Animals of Australia -- with thicker fur in cold climates -- blind, in caves -- extinct, of Australia Anomma Antarctic islands, ancient flora of Antechinus Ants attending aphides -- slave-making instinct -- neuters, structure of Apes, not having acquired intellectual powers Aphides attended by ants Aphis, development of Apteryx Arab horses Aralo-Caspian Sea Archeopteryx Archiac, M.de, on the succession of species Artichoke, Jerusalem Ascension, plants of Asclepias, pollen of Asparagus Aspicarpa Asses, striped -- improved by selection Ateuchus Aucapitaine, on land-shells Audubon, on habits of frigate-bird -- on variation in birds' nests -- on heron eating seeds Australia, animals of -- dogs of -- extinct animals of -- European plants in -- glaciers of Azara, on flies destroying cattle Azores, flora of Babington, Mr., on British plants Baer, Von, standard of Highness -- comparison of bee and fish -- embryonic similarity of the Vertebrata Baker, Sir S., on the giraffe Balancement of growth Baleen Barberry, flowers of Barrande, M., on Silurian colonies -- on the succession of species -- on parallelism of palaeozoic formations -- on affinities of ancient species Barriers, importance of Bates, Mr., on mimetic butterflies Batrachians on islands Bats, how structure acquired -- distribution of Bear, catching water-insects Beauty, how acquired Bee, sting of -- queen, killing rivals -- Australian, extermination of Bees, fertilizing flowers -- hive, not sucking the red clover -- hive, cell-making instinct -- Ligurian -- variation in habits Bees, parasitic -- humble, cells of Beetles, wingless, in Madeira -- with deficient tarsi Bentham, Mr., on British plants -- on classification Berkeley, Mr., on seeds in salt-water Bermuda, birds of Birds acquiring fear -- beauty of -- annually cross the Atlantic -- colour of, on continents -- footsteps, and remains of, in secondary rocks -- fossil, in caves of Brazil -- of Madeira, Bermuda, and Galapagos -- song of males -- transporting seeds -- waders -- wingless Bizcacha, affinities of Bladder for swimming, in fish Blindness of cave animals Blyth, Mr., on distinctness of Indian cattle -- on striped Hemionus -- on crossed geese Borrow, Mr., on the Spanish pointer Bory St.Vincent, on Batrachians Bosquet, M., on fossil Chthamalus Boulders, erratic, on the Azores Branchiae -- of crustaceans Braun, Prof., on the seeds of Fumariaceae Brent, Mr., on house-tumblers Britain, mammals of Broca, Prof., on Natural Selection Bronn, Prof., on duration of specific forms -- various objections by Brown, Robert, on classification Brown-Sequard, on inherited mutilations Busk, Mr., on the Polyzoa Butterflies, mimetic Buzareingues, on sterility of varieties Cabbage, varieties of, crossed Calceolaria Canary-birds, sterility of hybrids Cape de Verde Islands, productions of -- plants of, on mountains Cape of Good Hope, plants of Carpenter, Dr., on foraminifera Carthemus Catasetum Cats, with blue eyes, deaf -- variation in habits of -- curling tail when going to spring Cattle destroying fir-trees -- destroyed by flies in Paraguay -- breeds of, locally extinct -- fertility of Indian and European breeds -- Indian Cave, inhabitants of, blind Cecidomyia Celts, proving antiquity of man Centres of creation Cephalopodae, structures of eyes -- development of Cercopithecus, tail of Ceroxylus laceratus Cervulus Cetacea, teeth and hair -- development of the whalebone Cetaceans Ceylon, plants of Chalk formation Characters, divergence of -- sexual, variable -- adaptive or analogical Charlock Checks to increase -- mutual Chelae of Crustaceans Chickens, instinctive tameness of Chironomus, its asexual reproduction Chthamalinae Chthamalus, cretacean species of Circumstances favourable to selection of domestic products -- to natural selection Cirripedes capable of crossing -- carapace aborted -- their ovigerous frena -- fossil -- larvae of Claparede, Prof., on the hair-claspers of the Acaridae Clarke, Rev.W.B., on old glaciers in Australia Classification Clift, Mr., on the succession of types Climate, effects of, in checking increase of beings -- adaptation of, to organisms Climbing plants -- development of Clover visited by bees Cobites, intestine of Cockroach Collections, palaeontological, poor Colour, influenced by climate -- in relation to attacks by flies Columba livia, parent of domestic pigeons Colymbetes Compensation of growth Compositae, flowers and seeds of -- outer and inner florets of -- male flowers of Conclusion, general Conditions, slight changes in, favourable to fertility Convergence of genera Coot Cope, Prof., on the acceleration or retardation of the period of reproduction Coral-islands, seeds drifted to -- reefs, indicating movements of earth Corn-crake Correlated variation in domestic productions Coryanthes Creation, single centres of Crinum Croll, Mr., on subaerial denudation -- on the age of our oldest formations -- on alternate Glacial periods in the North and South Crosses, reciprocal Crossing of domestic animals, importance in altering breeds -- advantages of -- unfavourable to selection Cruger, Dr., on Coryanthes Crustacea of New Zealand Crustacean, blind air-breathers Crustaceans, their chelae Cryptocerus Ctenomys, blind Cuckoo, instinct of Cunningham, Mr., on the flight of the logger-headed duck Currants, grafts of Currents of sea, rate of Cuvier on conditions of existence -- on fossil monkeys Cuvier, Fred., on instinct Cyclostoma, resisting salt water Dana, Prof., on blind cave-animals -- on relations of crustaceans of Japan -- on crustaceans of New Zealand Dawson, Dr., on eozoon De Candolle, Aug.Pyr., on struggle for existence -- on umbelliferae -- on general affinities De Candolle, Alph., on the variability of oaks -- on low plants, widely dispersed -- on widely-ranging plants being variable -- on naturalisation -- on winged seeds -- on Alpine species suddenly becoming rare -- on distribution of plants with large seeds -- on vegetation of Australia -- on fresh-water plants -- on insular plants Degradation of rocks Denudation, rate of -- of oldest rocks -- of granite areas Development of ancient forms Devonian system Dianthus, fertility of crosses Dimorphism in plants Dirt on feet of birds Dispersal, means of -- during Glacial period Distribution, geographical -- means of Disuse, effect of, under nature Diversification of means for same general purpose Division, physiological, of labour Divergence of character Dog, resemblance of jaw to that of the Thylacinus Dogs, hairless, with imperfect teeth -- descended from several wild stocks -- domestic instincts of -- inherited civilisation of -- fertility of breeds together -- of crosses -- proportions of body in different breeds, when young Domestication, variation under Double flowers Downing, Mr., on fruit-trees in America Dragon-flies, intestines of Drift-timber Driver-ant Drones killed by other bees Duck, domestic, wings of, reduced -- beak of -- logger-headed Duckweed Dugong, affinities of Dung-beetles with deficient tarsi Dyticus Earl, Mr., W., on the Malay Archipelago Ears, drooping, in domestic animals -- rudimentary Earth, seeds in roots of trees -- charged with seeds Echinodermata, their pedicellariae Eciton Economy of organisation Edentata, teeth and hair -- fossil species of Edwards, Milne, on physiological division of labour -- on gradations of structure Edwards, on embryological characters Eggs, young birds escaping from Egypt, productions of, not modified Electric organs Elephant, rate of increase -- of Glacial period Embryology Eozoon Canadense Epilipsy inherited Existence, struggle for -- condition of Extinction, as bearing on natural selection -- of domestic varieties Eye, structure of -- correction for aberration Eyes, reduced, in moles Fabre, M., on hymenoptera fighting -- on parasitic sphex -- on Sitaris Falconer, Dr., on naturalisation of plants in India -- on elephants and mastodons -- and Cautley on mammals of sub-Himalayan beds Falkland Islands, wolf of Faults Faunas, marine Fear, instinctive, in birds Feet of birds, young molluscs adhering to Fertilisation variously effected Fertility of hybrids -- from slight changes in conditions -- of crossed varieties Fir-trees destroyed by cattle -- pollen of Fish, flying -- teleostean, sudden appearance of -- eating seeds -- fresh-water, distribution of Fishes, ganoid, now confined to fresh water -- ganoid, living in fresh water -- electric organs of -- of southern hemisphere Flight, powers of, how acquired Flint-tools, proving antiquity of man Flower, Prof., on the larynx -- on Halitherium -- on the resemblance between the jaws of the dog and Thylacinus -- on the homology of the feet of certain marsupials Flowers, structure of -- in relation to crossing -- of composite and umbelliferae -- beauty of -- double Flysch formation, destitute of organic remains Forbes, Mr.D., on glacial action in the Andes Forbes, E., on colours of shells -- on abrupt range of shells in depth -- on poorness of palaeontological collections -- on continuous succession of genera -- on continental extensions -- on distribution during Glacial period -- on parallelism in time and space Forests, changes in, in America Formation, Devonian -- Cambrian -- intermittent -- thickness of, in Britain Formica -- rufescens -- sanguinea -- flava, neuter of Forms, lowly organised, long enduring Frena, ovigerous, of cirripedes Fresh-water productions, dispersal of Fries on species in large genera being closely allied to other species Frigate-bird Frogs on islands Fruit-trees, gradual improvement of -- in United States -- varieties of, acclimatised in United States Fuci, crossed Fur, thicker in cold climates Furze Galapagos Archipelago, birds of -- productions of Galaxias, its wide range Galeopithecus Game, increase of, checked by vermin Gartner on sterility of hybrids -- on reciprocal crosses -- on crossed maize and verbascum -- on comparison of hybrids and mongrels Gaudry, Prof., on intermediate genera of fossil mammals in Attica Geese, fertility when crossed -- upland Geikie, Mr., on subaerial denudation Genealogy, important in classification Generations, alternate Geoffroy St.Hilaire, on balancement -- on homologous organs Geoffroy St.Hilaire, Isidore, on variability of repeated parts -- on correlation, in monstrosities -- on correlation -- on variable parts being often monstrous Geographical distribution Geography, ancient Geology, future progress of -- imperfection of the record Gervais, Prof., on Typotherium Giraffe, tail of -- structure of Glacial period -- affecting the North and South Glands, mammary Gmelin, on distribution Godwin-Austin, Mr., on the Malay Archipelago Goethe, on compensation of growth Gomphia Gooseberry, grafts of Gould, Dr.Aug.