The Origin of Species

bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a struggle for life, and as a consequence to Natural Selection, entailing divergence of character and the extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.

Glossary of the Principal Scientific Terms Used in the Present Volume

(I am indebted to the kindness of Mr. W. S. Dallas for this Glossary, which has been given because several readers have complained to me that some of the terms used were unintelligible to them. Mr. Dallas has endeavoured to give the explanations of the terms in as popular a form as possible.)

Aberrant

Forms or groups of animals or plants which deviate in important characters from their nearest allies, so as not to be easily included in the same group with them, are said to be aberrant.

Aberration (in Optics)

In the refraction of light by a convex lens the rays passing through different parts of the lens are brought to a focus at slightly different distance: this is called Spherical Aberration; at the same time the coloured rays are separated by the prismatic action of the lens and likewise brought to a focus at different distance: this is Chromatic Aberration.

Abnormal

Contrary to the general rule.

Aborted

An organ is said to be aborted, when its development has been arrested at a very early stage.

Albinism

Albinos are animals in which the usual colouring matters characteristic of the species have not been produced in the skin and its appendages. Albinism is the state of being an albino.

Algae

A class of plants including the ordinary seaweeds and the filamentous freshwater weeds.

Alternation of Generations

This term is applied to a peculiar mode of reproduction which prevails among many of the lower animals, in which the egg produces a living form quite different from its parent, but from which the parent-form is reproduced by a process of budding, or by the division of the substance of the first product of the egg.

Ammonites

A group of fossil, spiral, chambered shells, allied to the existing pearly Nautilus, but having the partitions between the chambers waved in complicated patterns at their junction with the outer wall of the shell.

Analogy

That resemblance of structures which depends upon similarity of function, as in the wings of insects and birds. Such structures are said to be Analogous, and to be Analogues of each other.

Animalcule

A minute animal: generally applied to those visible only by the microscope.

Annelids

A class of worms in which the surface of the body exhibits a more or less distinct division into rings or segments, generally provided with appendages for locomotion and with gills. It includes the ordinary marine worms, the earthworms, and the leeches.

Antennae

Jointed organs appended to the head in Insects, Crustacea and Centipedes, and not belonging to the mouth.

Anthers

The summits of the stamens of flowers, in which the pollen or fertilising dust is produced.

Aplacentalia

Aplacentata

Aplacental Mammals

See Mammalia.

Archetypal

Of or belonging to the Archetype, or ideal primitive form upon which all the beings of a group seem to be organised.

Articulata

A great division of the Animal Kingdom characterised generally by having the surface of the body divided into rings called segments, a greater or less number of which are furnished with jointed legs (such as Insects, Crustaceans and Centipedes).

Asymmetrical

Having the two sides unlike.

Atrophied

Arrested in development at a very early stage.

Balanus

The genus including the common Acorn-shells which live in abundance on the rocks of the seacoast.

Batrachians

A class of animals allied to the Reptiles, but undergoing a peculiar metamorphosis, in which the young animal is generally aquatic and breathes by gills. (Examples, Frogs, Toads, and Newts.)

Boulders

Large transported blocks of stone generally embedded in clays or gravels.

Brachiopoda

A class of marine Mollusca, or soft-bodied animals, furnished with a bivalve shell, attached to submarine objects by a stalk which passes through an aperture in one of the valves, and furnished with fringed arms, by the action of which food is carried to the mouth.

Branchiae

Gills or organs for respiration in water.

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