Didelphia
one of the three primary divisions into which the class Mammalia is divided, when the structure of the reproductive organs is taken as a basis for classification; the other two being the Ornithodelphia (Monotremata) and the Monodelphia. Didelphia comprises the Marsupialia or those non-placental mammals in which the uterine dilations of the oviducts continue distinct throughout life, opening into two separate vaginæ, which in turn open into a urogenital canal, distinct from the rectum, though embraced by the same sphincter muscle. The young of this subclass are born imperfect, or, as it were, prematurely, and are carried in the pouch or second womb till perfect.