Mammalian Character of Mam — Common Descent of all Mammals from a Single Parent-form (promammalian). — Bifurcation of the Amnion Animals into Two Main Lines: on the one side, Rep tiles and Birds, on the other, Mammals. — Date of the Origin of Mammals: the Trias Period. — The Three Main Groups or Sub classes of Mammals: their Genealogical Relations — Sixteenth Ancestral Stage Cloacal Animals (monotremata, or Ornithodelphia). — 'l'he Extinct Primitive Mammals (promammalz'a) and the Extant Beaked Animals (ornithostoma). — Seventeenth Ancestral Stage Pouched Animals (marsupialia, or Dz'delphia). — Extinct and Extant Pouched Animals — Their Intermediate Position between Mono tremes and Placental Animals — Origin and Structure of Placental Animals (placentalia, or — Formation of the Pla centa. — The Deciduous Embryonic Membrane (decidua). — Group of the Indecidua. And of the Deciduata. — The Formation of the Decidua (vera, serotina, re?exa) in Man and in Apes — Eighteenth Stage: Semi-apes (prosimice). — Nineteenth Stage: Tailed Apes (menocerca). — Twentieth Stage Man-like Apes (anthropoides). Speechless and Speaking Men (mali. Homines)