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Von Baer, towards whom all zoologists feel so profound a respect, expressed about the year 1859 (see Prof. Rudolph Wagner, ‘Zoologisch-Anthropologische Untersuchungen,’ 1861, s. 51 ) his conviction, chiefly grounded on the laws of geographical distribution, that forms now perfectly distinct have descended from a single parent-form.

In June, 1859, Professor Huxley gave a lecture before the Royal Institution on the ‘Persistent Types of Animal Life.’ Referring to such cases, he remarks, “It is difficult to comprehend the meaning of such facts as these, if we suppose that each species of animal and plant, or each great type of organisation, was formed and placed upon the surface of the globe at long intervals by a distinct act of creative power; and it is well to recollect that such an assumption is as unsupported by tradition or revelation as it is opposed to the general analogy of nature. If, on the other hand, we view ‘Persistent Types’ in relation to that hypothesis which supposes the species living at any time to be the result of the gradual modification of pre-existing species a hypothesis which, though unproven, and sadly damaged by some of its supporters, is yet the only one to which physiology lends any countenance; their existence would seem to show that the amount of modification which living beings have undergone during geological time is but very small in relation to the whole series of changes which they have suffered.”

In December, 1859, Dr. Hooker published his ‘Introduction to the Australian Flora: In the first part of this great work he admits the truth of the descent and modification of species, and supports this doctrine by many original observations.

The first edition of this work was published on November 24th, 1859, and the second edition on January 7th, 1860.

GLOSSARY OF THE PRINCIPAL SCIENTIFIC TERMS USED IN THE PRESENT VOLUMEv

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 distances, 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 distances, 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 sea-weeds and the filamentous fresh-water 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