_Genotype_: The total assemblage of germinal factors transmitted by a given species of organism, that is, the complete complex of genes synthesized in the zygote and perpetuated by equation-divisions in the somatic cells. Hence the basic germinal or hereditary constitution of an organism or group of organisms. _Germ Cells_: Cells specialized for reproduction as contrasted with other vital functions, _e.g._, spores and gametes. _Germ-plasm_: The material basis of inheritance. _Glacial Epoch_: After the close of the Tertiary period, Europe and North America are said to have been covered with vast ice sheets known as continental glaciers (the result of great climatic changes in the Northern hemisphere). As the weather varied these ice sheets advanced and retreated, the retreats corresponding to the so-called Interglacial intervals. Four Glacial and three Interglacial stages are distinguished, and it was during the Second and Third of these Interglacial stages that Palæolithic Man is alleged to have entered Europe. _Golgi Bodies_: A cytoplasmic apparatus consisting, in its localized form, of a network, and, in its dispersed form, of scattered granules. It appears to divide on the mitotic spindle, and seems to have some important function connected with secretion. _Habitat_: The locality in which a given animal or plant normally lives. _Hallux_: The great toe, opposable in the ape, but not in man. _Heredity_: “The appearance in offspring of characters whose differential causes are in the germ cells” (Conklin). _Heterozygous_: Hybrid,—the condition in which the chromosomal genes paired by syngamy in the zygote are unlike. _Homologous Chromosomes_: Corresponding chromosomes of the same synaptic pair, being of paternal and maternal origin respectively. _Homozygous_: Pure,—the condition in which the chromosomal genes paired in the zygote by syngamy are alike. _Hormone_: An internal secretion elaborated in the endocrine or ductless glands and diffused in the blood stream for the purpose of influencing the activities or metabolism of parts of the organism at a distance from the source of the hormone, _e. g._, secretin, gastrin, adrenalin, etc. _Hydrotheca_: The cuplike extension of the perisarc (skeletal sheath) surrounding the hypostome (oral cone) and tentacles of certain polyps. _Hyloblatic_: Resembling the gibbon. _Lemurs_: Four-handed animals allied to the Insectivora, with curved nostrils and a claw instead of a nail on the first finger of the rear hands. _Lethals_: A genetical term for hereditary factors (genes) which cause the death of the gametes or the zygotes that contain them. In the case of zygotes, death results from the homozygous, but not from the heterzygous, condition. _Linin_: Same as oxychromatin.