As a rule there is no allantoic placenta forming the means of communication between the blood of the parent and the foetus, and when such a structure does occur its development is incomplete.
It is urged that the imperfect placenta of the bandicoots instead of being vestigial, may be an instance of parallelism, and that in marsupials generally the allantois failed to form a placental connexion.
Finally, there is the hypothesis that marsupials are the descendants of placentals, in which case, as was suggested by its discoverer, the placenta of the bandicoots would be a true vestigial structure.
The stomach is simple, the caecum large and capacious, the placenta diffused, and the teats inguinal.
P, a thickened line on the walls forming the placenta; c, calyx; d, ovary; s, hooded stigma terminating the short style.
P, placenta; o, ovules; s, suture, or median line of carpel.
Toffs is largely developed, and the placenta, so far as known, is nondeciduate, the chorionic villi being either evenly diffused or collected in groups or cotyledons (in Pecora).
Placenta diffused or cotyledonary.
Modification of placenta from simple diffused to cotyledonary form.
Placenta diffuse, without cotyledons.
The stomach is simple or somewhat complex, and the placenta diffused.
The placenta is discoidal and deciduate.
Female has six teats, of which four are inguinal and two axillary, and the placenta is zonary and deciduous.
Malformations of the pelvis, accidental injuries and the diseases and displacements to which the uterus is liable, on the one hand; and, on the other, various morbid conditions of the ovum or placenta leading to the death of the foetus, are among the direct local causes.
When placed on the stigma, under favourable circumstances, the pollen-grain puts forth a pollen-tube which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the mouth of an ovule.
The ovary contains one or more ovules borne on a placenta, which is generally some part of the ovary-wall.
In Casuarina, Juglans and the order Corylaceae, the pollen-tube does not enter by means of the micropyle, but passing down the ovary wall and through the placenta, enters at the chalazal end of the ovule.
Placenta with few cotyledons.
Placenta with many cotyledons.
The petaloid perianth consists of two series, each with three members, which are joined below into a longer or shorter tube, followed by one whorl of three stamens; the inferior ovary is three-celled and contains numerous ovules on an axile placenta; the style is branched and the branches are often petaloid.
The placenta is diffuse, not cotyledonary.
The superior ovary - half-inferior in Samolus - bears a simple style ending in a capitate entire stigma, and contains a free-central placenta bearing generally a large number of ovules, which are exceptional in the group Gamopetalae in having two integuments.
While most of the species are of interest chiefly to the conchologist, there are a number of edible forms. The shells of Placuna placenta, L., split into thin flat plates and, cut into small squares, are almost universally used in place of window glass.
Near affinity; and while more nearly related to the Marsupialia (q.v.), in which an imperfect allantoic placenta is sometimes developed, it is broadly distinguished therefrom by the invariable presence of a functional placenta by the aid of which the foetus is nourished throughout the greater portion of intra-uterine life.
In Araucaria the cone-scale is regarded as consisting of a flat carpel, of which the placenta has not grown out into the scale-like structure.