• Webster's Revised Unabridged Dictionary
    • n. pl Didelphia (Zoöl) The subclass of Mammalia which includes the marsupials. See Marsupialia.
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Century Dictionary and Cyclopedia
    • didelphia The Marsupialia or marsupial implacental mammals; one of the three subclasses of Mammalia, the other two being Ornithodelphia and Monodelphia. They have no placenta, and the womb double, whence the name —that is, the uterine dilatations of the oviducts continue through life distinct from each other, right and left, and open into two distinct vaginæ, which debouch in turn into a urogenital sinus, forming, with the termination of the rectum, a common cloaca embraced by the external sphincter muscle, and in the male lodging the penis, which thus appears to protrude from the anus. The female has usually an abdominal pouch or marsupium, formed by a fold of the skin of the belly, in which the mammary glands open, and into which the blind, naked, and imperfectly developed young are received and carried for some time hanging to the nipples. The scrotum of the male occupies a similar position. Both the marsupium and the scrotum are supported to some extent by the marsupial bones characteristic of this group, being ossifications in the tendon of the external oblique muscle of the abdomen, articulated with the pubes. A cremasteric muscle in relation with these bones acts in the female upon the mammary glands, effecting their compression, and consequently the flow of milk into the mouths of the helpless young. There are true teeth of two or three kinds. The coracoid is reduced to a process of the scapula, as in ordinary mammals, not reaching the sternum, as in monotremes. The corpus callosum is rudimentary or wanting, and the brain relatively small. The Didelphia are among the oldest known mammals, and formerly had an extensive range, but are now mainly confined to the Australian region, the American opossums offering the principal exception. Some of the extinct forms were of great size: the kangaroos are the largest living representatives. The marsupials are notable for their great physiological adaptation to all the modes of life of ordinary mammals, their structure being modified in relation to the carnivorous, the herbivorous, the rodent, and other habitudes, and their modes of progression and general economy being no less diverse. There is but one order, Marsupialia (which see).
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Chambers's Twentieth Century Dictionary
    • n.pl Didelphia dī-del′fi-a the marsupialia, or marsupial implacental mammals, one of the three sub-classes of Mammalia
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Webster's Revised Unabridged Dictionary
NL., fr. Gr. = matrix, uterus
Chambers's Twentieth Century Dictionary
Gr. di-, double, delphys, womb.


In literature:

The Marsupials have been sometimes called the Didelphia.
"The Cambridge Natural History, Vol X., Mammalia" by Frank Evers Beddard