=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. =Compositae.=—Plants in which the inflorescence consists of numerous small flowers brought together into a dense head, the base of which is enclosed by a common envelope (e.g. the Daisy, Dandelion, &c.). =Congenital characters.=—_See_ Plasmogenetic characters. =Conjugation.=—This term is applied to a process observed in the Protozoa (q. v.), which seems to correspond to the sexual reproduction of the Metazoa (q. v.). The majority of the Protozoa cannot long continue to reproduce themselves a-sexually without becoming degenerate, or rather without becoming altogether extinct. Two individuals (as a rule) consequently unite either temporarily or permanently. In the former case, an exchange of material is effected; and in the latter, complete fusion takes place. =Correlation.=—The normal coincidence of one phenomenon, character, &c., with another. =Cytoplasm.=—_See_ pp. 30 and 32. =Determinant.=—_See_ p. 123. =Ectoblast.=—Syn. of epiblast and ectoderm. The general result of the division of a fertilized ovum is a two-layered ball of cells (a gastrula). The outer layer is called the ectoblast and the inner layer the entoblast. (See _Darwin and after Darwin_, p. 137 _et seq._). =Embryology.=—Hence embryogenesis, &c. The study of the development or the early growth of the individual. =Entoblast.=—Syn. of hypoblast and endoderm. _See_ Ectoblast. =Epigenesis= (=Harvey=).—The theory that organisms are formed by the development of the egg itself, and not by the expansion of a miniature within the egg (preformation). =Fallopian Tubes.=—The tubes through which the spermatozoa pass to effect fertilization, and through which the ova pass from the ovary to the uterus. =Fission.=—Syn. of fissiparous separation. The breaking into two (without karyokinesis—q. v.) of a cell, which has, by overgrowth, disturbed its physiological equilibrium. This process is almost mechanical. =Formative material.=—_See_ p. 56. =Gemmation.=—That form of a-sexual reproduction known as budding. =Gemmules= (=Darwin=).—Minute granules, formed by the division of the general body-cells, which are supposed to be dispersed throughout the entire system. These themselves multiply by division, and are collected from all parts of the body to constitute the sexual elements. =Germ-plasm.=—_See_ p. 32.