After the mother had rested quietly for a short time, we again examined her, but found the young one still detached, moving more vigorously than before. On an examination two days afterwards the marsupium was found empty : the young one had died and had pro bably been removed by the mother.
Thus the period of uterine gestation, the condition of the new-born young, and the pro bable mode of its transference to the nipple being determined in the genus Macropus, it next remained to be determined how the embryo was nourished in utero. The means of giving the required solution were shortly after afforded by specimens of the impregnated uterus, trans mitted to me by Mr. George Bennett, Captain Grey, and Dr. Sweatman. The first was of the Macropus major, nearly two-thirds of uterine gestation having been completed ; the second was of the .A.lacropus penieillatus, at about the same or somewhat earlier period of gestation ; the third exhibited the uterine foetus at nearly the completion of that period of its existence.
Before, however, giving the summary of what I have elsewhere recorded respecting the uterine development of the Marsupialia, a de scription of the ovarian ovum must be pre mised.
In the Kangaroo this part agrees in all essen tial points with the observed ovarian ova of placental Mammalia : the main modification is the greater proportion of vitelline fluid and globules, and the smaller proportion of fluid between the external membrane of the ovum (vitelline membrane) and the ovarian vesicle, or lining membrane of the ovisac.
In a female Maeropus Parryi, the ovum from the largest ovisac of the left ovarium measured of a line in diameter, the germinal vesicle of a line in diameter.
We are at present ignorant of the changes that take place in the development of the ovum between the period of impregnation until about the twentieth day of uterine gestation. At this time, in the great Kangaroo ( Macropus major), the uterine foetus (fig. 138) measures eight lines from the mouth to the root of the tail; the mouth is widely open (fig. 141); the tongue large and protruded; the nostrils are small round apertures; the eyeball not yet wholly defended by the palpebral folds; the meatus auditoriusexternus is not provided with an auricle; the fore-extremities are the largest and strongest ; they are each terminated by five well-marked digits ; those of the hind legs are not yet developed ; the cervical fold of the mucous layer or the branchial fissure is still unenclosed by the integument. The tail is
two lines long, thick and strong at the com mencement; impressions of the ribs are visi ble at the sides of the body; the membranous tube of the spinal marrow may be traced along the back between the ununited elements of the vertebral arches ; posterior to the um bilical chord there is a small projecting penis, and behind that, on the same prominence, is the anus. This foetus and its appen dages were enveloped in a large chorion, puckered up into numerous folds, some of i which were insinuated between folds of the vascular lining membrane of the uterus, but the greater portion was collected into a wrinkled mass. The entire ovum was re moved without any opposition from a placental or villous adhesion to the uterus. The chorion (a, a, fig. 141) was extremely thin and lacera ble; and upon carefully examining its whole outer surface, no trace of villi or of vessels could be perceived. Detached portions were then placed in the field of a microscope, but without the slightest evidence of vascularity being discernible. The next membrane, whose nature and limits will be presently described, was seen extending from the umbilicus to the inner surface of the chorion, and was highly vascular. The foetus was immediately enve loped in a transparent amnios.
On turning the chorion away from the foetus, it was found to adhere to the viicular mem brane above-mentioned, into wffh the um bilical stem suddenly expanded. With a slight effort, however, the two membranes could be separated from each other, without laceration, for the extent of an inch; but at this distance from the umbilicus the chorion gave way on every attempt to detach it from the internal vascular membrane, which here was plainly seen to terminate in a well-defined ridge, formed by the trunk of a bloodvessel.