Asexual Reproduction.—In which there is no liberation of special germ cells containing the potentiality of the adult organism, but in which the same object is effected by the liberation of buds, overgrowths, &c., which develop into the parent form. There are many forms of a-sexual reproduction.
Atavism.—The abnormal occurrence in existing species of characters which were peculiar to ancestral species, e.g., see Darwin and after Darwin, 2nd ed., Part I, p. 94.
Biophore.—See p. 123.
Blastogenetic characters.—See Plasmogenetic characters.
Calyx.—The outermost covering of the flower, which protects it before opening. Its position and precise function vary.
Cell nucleus.—A spherical or ovoid body embedded in the cell protoplasm, which has important functions in cell division and in reproduction. It consists of chromatin and achromatin. There are often several nuclei in one cell, whilst some cells have not been shown to have a nucleus at all.
Cessation of Selection (Romanes).—See Panmixia.
Chromatin threads.—Immediately before a cell divides the nucleus is resolved into chromatin fibres or threads and an achromatin matrix. These chromatin fibres are then marshalled into either rods or loops, &c., as the division of the cell proceeds (see Darwin and after Darwin, figs. 36, 37, and 38). Subsequent changes in the threads conclude the division (for a description of which consult the account above).
Chromosomes.—See Chromatin threads.