MARSUPIALIA. 



323 



pouch was by the mouth of the mother. Her 

 fore-paws, in this case, would be used, not 

 for the transport of the young, but for keeping 

 the mouth of the pouch open for its reception, 

 it being deposited therein by the mouth, and so 

 held over a nipple until the mother had felt it 

 grasping the sensitive extremity of the nipple. 



This means of removal is consistent with 

 analogy ; dogs, cats, mice, all transport their 

 young from place to place with the mouth. In 

 the case of the kangaroo, it may be supposed 

 that the foetus would be held by the lips only, 

 not the teeth, on account of its delicate con- 

 sistence. Whether this theory, suggested by 

 witnessing the actions of the mother after an 

 artificial separation of the Marsupial foetus, 

 be correct, must be confirmed by actual obser- 

 vation. There is no internal passage from the 

 uterus to the pouch : the month of the vagina 

 cannot be brought into contact with that of the 

 pouch, either by muscular contraction in the 

 living or by any force of stretching in the dead 

 kangaroo : as the young was proved by the 

 result of this experiment not to have the power 

 of itself to regain the nipple, d fortiori we 

 may conclude that it could not transfer itself 

 from the vulva to the interior of the pouch and 

 to the apex of the nipple : the fore-paws of 

 the Kangaroo would not so effectually protect 

 the tender embryo from the external air as the 

 mouth, nor so safely ensure its passage to the 

 pouch, notwithstanding that they are adroitly 

 used in grasping objects, being similar, in 

 respect of the extent and freedom of motion of 

 the digits, to the fore-paws of the Rodents. 



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. Swealman. The first was of the 

 Macropus major, nearly two-thirds of uterine 

 gestation having been completed ; the second 

 was of the Macropus penicillatus, 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 



* Proceedings of the Zool. Society, 1833. Philos. 

 Trans. 1834. 



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 Macropus Parry i, the ovum from 

 the largest ovisac of the left ovarium measured 

 j'yth of a line in diameter, the germinal vesicle 

 T ] 5 th 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 (Jig. 138) measures eight 

 lines from the mouth to the root of the tail ; 

 the mouth is widely open (Jig. 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 fetus and its appen- 

 dages were enveloped in a large chorion, 

 puckered up into numerous folds, some of 

 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, Jig. 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 vascular m|em- 

 brane above-mentioned, into which 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. 



When the whole of the vascular membrane 



Y 2 



