The Monotremata are regarded as primitive mammals since they exhibit skeletal structures found in therapsid reptiles, and physiological processes and structures found in living Sauropsida. At the same time one finds in the monotremes characters as advanced as any in the Metatheria and Eutheria. Amongst these are parameters of lactation and structure of the mammary glands; those entities are discussed. Since researches of Kielan-Jaworowska (1971) have shown that Cretaceous multituberculates are more closely related to monotremes than to other Mesozoic mammals it is suggested that the parameters of lactation in multituberculates were similar to those of their living relatives - the monotremes. The notion is supported by the evidence (Kielan-Jaworowska 1979) that Cretaceous multituberculates had tiny altricial young as do the monotremes.

Key words: Monotremata, lactation, Multituberculata, Cretaceous.