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.
Litopterna: A suborder of extinct ungulate mammals from the Miocene and Pliocene of South America resembling horses or llamas.