[Adaptational evolution of embryogenesis and adult placental individuals].

On the basis of a comparative morphological and embryological analysis the author concludes that lower mammals (ovipositors and marsupials) and higher mammals should not be united into a single class. Two classes should be distinguished: 1) lower mammals including modern ovipositor animals and marsupial animals and fossilized Multituberculata, Triconodonta, Symmetrodonta and Pantotheria; and 2) higher mammals or placental animals.