DRIESCH, experiments on eggs, 54; separation of segmentation spheres, 60. E Echinoderms, a group of marine animals, of which the star-fish is the most familiar type, eggs of, 54. Echinoidea, a group of echinoderms, 61. Ectoderm, the tissue in an adult derived from the epiblast (which see), 19. Egg, relation between structure and division of, 94; specific character of, 135. EMERY, on polymorphism in ants, 128. Endoderm, the tissue in an adult, derived from the hypoblast (which see), 19. Enfoldment. See Evolution. Epiblast. In the development of all multicellular animals, the young embryo soon becomes divided into two sets of cells, the epiblast and hypoblast; where a gastrula is formed, the outer layer of cells is the epiblast, the inner layer the hypoblast, xviii. Epigenesis, the doctrine that the formation of a new individual is not the mere out-growing of particles hidden in the egg-cell, but the result of moulding external forces, xiii; Roux's definition of, 7; Weismann's denial of, 9; epigenetic explanation of stages in development, 98; summary of Hertwig's acceptance of, 136. Evolution. Originally the term was applied, not to the origin of existing forms of life from common ancestors, but to the doctrine that every living creature contained within it the whole series of its future descendants, and that the growth of a living creature was evolving of one of these enfolded miniatures, xiii, 1, 2, 3; Roux's contrast of, with epigenesis, 6; the new evolution, 10; Hertwig's partial agreement with, 135, 136. Experiment, Weismann's caution against, 10. F Fertilisation, the union of the nuclear matter of a male cell with the nuclear matter of a female cell, xii, xiv. Foraminifera, a group of protozoa provided with shells, 44. FOREL, on eyes of ants, 126. Frogs' eggs, Hertwig's experiments upon; development of, under compression, 57-60. Funaria, reproduction from chopped pieces, 46. G Galls, 50. Gastrula, an early embryonic stage, most simply formed from the blastosphere by the invagination of one side of the wall, and consisting of a hollow sac, the walls of which are formed by two layers of cells, xviii, 60; formation of, 99. Gemmules. See Pangenesis. Germ, the youngest embryonic stage of an individual or organ, 10. Germplasm, the substance supposed to be the material bearer of inherited qualities: Weismann's conception of, viii, 20; identification of, with nuclear matter, 21; account of Weissmann's theory, 21-28. Germ-tracks, the hypothetical paths along which germplasm passes in an unaltered condition during development, 27; objections to, 81. GOEBEL, on plasticity of plants, 120. Grafting, 68, 70; of Hydra, 72; bone-grafting, 73, 74; skin-grafting, 74, 120, 121. GRASSI, polymorphism due to food, 129. Gregarines, a group of parasitic protozoa, development of, 41. H HAACKE, declaration that Hertwig is evolutionary, 135. Hæmoglobin, the red colouring matter of blood, 75.