320 



MARSUPIALIA. 



tion, 8cc. This theory, however, was aban- 

 doned, or at least considerably modified after 

 the publication of Dr. Barton's letters relative 

 to the breeding of the Opossum. The product 

 of marsupial generation is then stated by M. 

 Geoffrey to quit the uterus in the condition of a 

 gelatinous ovulum, comparable toa Medusa,and 

 to become organically connected with the nipple 

 by continuity of vessels. He supposed, there- 

 fore, that a flow of blood followed the detach- 

 ment of the mammary fcetus from the nipple,* 

 and even speculates upon the signification of 

 the thyroid gland, on the strength of this hypo- 

 thetical confluence of the maternal and foetal 

 vascular systems in the marsupial tribe, f 



In another essay M. Geoffrey abandons this 

 opinion, it having been proved by repeated 

 observation that the adhesion of the foetus to 

 the nipple is by simple contact merely ;J and 

 finally, he falls into the opposite extreme, and 

 from some appearances of an urachus which 

 were pointed out to him in a very small foetus 

 of an American Opossum, he describes them 

 as vestiges of a placental organization. 



Mr. Morgan, in his elaborate and excellent 

 Memoirs on the Structure and Development of 

 the Mammary Organs of the Kangaroo, bears 

 testimony to the simply mechanical mode of 

 attachment between the mammary fcetus and 

 the nipple in the Kangaroo, and was the first 

 to show that the young animal, in its blind 

 and naked condition, prior to the act of volun- 

 tary detachment, the birth ' a la maniere des 

 Marstipiaux,' as it is called by M. Geoflfroy, 

 would bear a separation from the nipple for 

 two hours, and voluntarily regain its hold. The 

 mammary foetus of the Kangaroo on which Mr. 

 Morgan experimented was nearly the size of a 

 fully grown Norway rat. Mr. Collie, surgeon 

 R.N. in a letter addressed from New South 

 Wales, and published in the Zoological Journal, 

 (No. xvm. p. 239,) obtained the same result 

 in detaching from the nipple of a smaller 

 species of Kangaroo ( J\Jacroptis Brunii) a 

 mammary fcetus, not two inches in length : he 

 says, " I gently pressed with the tip of my 

 finger the head of the little one away from the 

 teat of which it had hold, and continuing press- 

 ing a little more strongly for the space of a 

 minute altogether, when the teat which had 

 been stretched to more than an inch came out 

 of the young one's mouth, and showed a small 

 circular enlargement at its tip, well adapting it 

 for being retained by the mouth of the sucker." 



* Geoffrey St. Hilaire, in detailing some observa- 

 tions on a Kangaroo in the ' Annales des Sciences,' 

 observes, " car le sang aper9U a la litiere est un 

 indice qu'a ce moment le ioetus s'est detache de la 

 tetine et qu'il est ne definitivement a la maniere des 

 marsupiaux." Vol. ix. p. 342, 1827. 



t " Des vaisseaux nourriciers se repandroient-ils 

 des parties du pharynx le long et entre les lames de 

 la trachee artere pour entrer le coeur, et (conjecture 

 de M. Serros) le gland thyroide seroit-il le point 

 de leur reunion?" Geoff. St. Hilaire, Memoires du 

 Museum, torn. xix. p. 406, 1822. 



\ Art. Marsupiaux, Diet, des Sciences Nat. torn. 

 xix. 1823. 



Transactions of the Linnxan Society, vol. xvi. 

 pp. 61, 455. 



" An hour afterwards the young was ob- 

 served still unattached, but in about two hours 

 it had hold of the teat, and was actively em- 

 ployed sucking." 



Dr. Barton's very interesting observations on 

 the American Opossum are as follows : " The 

 female Didelphis Woapink sometimes produces 

 sixteen young ones at a birth. I have actually 

 seen this number attached to the teats, but 

 never a greater number. When they are first 

 excluded from the uterus, they are not only 

 very small but very obscurely shaped. The 

 place of the future eyes is merely marked by 

 two pale bluish specks; we see no ears; in 

 short the animal is a mere mis-shaped embryon. 

 Its mouth, which is afterwards to become very 

 large, is at first a minute hole, nearly of a trian- 

 gular form, and just of a sufficient size to 

 receive the teat, to which the little creature 

 adheres so firmly, that it is scarcely matter of 

 surprise that Beverly* and other writers have 

 asserted that the young grow fast to the teats. 



" It is not true that the young cannot be 

 detached from the mother without the loss of 

 blood ; I can assert the contrary from many ex- 

 periments made upon embryons weighing nine 

 grains and upwards. I have fully satisfied 

 myself as to all the various circumstances, both 

 in the structure and in the exertions of the 

 minute animal, which enable it, while yet a 

 mere speck of living matter, to cling so firmly 

 to the fountain of its support. 



" The wonderful little Didelphis is 



by no means the inanimate or the passive l.e.ng 

 some physiologists and naturalists have repre- 

 sented it.f 



" The toes of the fore-feet of the new bo; n 

 embryon opossum are furnished with sharp and 

 hard nails or claws, but this is not the case 

 with the hind-feet. The latter are for some 

 weeks of little use to the animal; but by means 

 of the former it is enabled to cling most firmly 

 to the teat, and especially to the hair in the 

 marsupium immediately around the teat. 



" An opossum-embryon, or foetus, which 



weighed sixty-seven grains, lived upwards of 

 thirty hours after I had detached it from the 

 teat. Another which weighed 116 lived thirty- 

 eight hours, at which time I killed it by putting 

 it in spiiits. 



" Su perforation (I should perhaps in strict 

 propriety say uterine, superfoetation) is wholly 

 incompatible with the established laws of the 

 economy of the Didelphis. But Nature, always 

 provident, wastes no time. While, therefore, 

 the first litter of young opossums are fast ap- 

 proaching to their adult slate, the mother ac- 

 cepts the ardour of the male; she is impreg- 

 nated ; and after a gestation which is not, I 

 think, remarkably short, if we consider the 

 small size of the embryons when they are ex- 

 cluded from the uterus, the marsupium is des- 

 tined to perform the office of a second, I was 

 going to say a more important, uterus ; just at 

 the time when the first litter have attained such 

 a size that they are no longer (one or two of 



* History of Virginia, p. 136, 1722. 

 t Pennant, Arctic Zool. i, p. 84. 



