4i4> [April, 



osteological characters of the latter species have been so accurately described 

 and delineated that little remains to be added in this department. 



3. The organs of generation being found perfect and adapted to their peculiar 

 uses — the double uterus to the bifurcated organ of the male — should have in 

 themselves been sufficient to have thrown doubts on the assertions of our early 

 authors — Marcgrave, Pison, Valentyn, Beverly, the Marquis of Chastellux, 

 Pennant, and others — that "the pouch was the matrix of the young opossum, 

 and that the mammsc aie, with regard to the young, what stalks are to their 

 fruits." 



3. The mode of copulation, although differing from that of the majority of 

 quadrupeds, is far from being the only exception to a general law ; our porcupine 

 (Hystrix dorsata) may be cited as another instance. In this respect the actions 

 of animals correspond with their peculiar organization, and the structure of the 

 genital organs, as well as the whole anatomy of the opossum, are in accordance 

 with this habit. 



4. The question propounded in 1819, to naturalists, by Geoffroy, "Are the 

 pouched animals born attached to the teats of the mother?" is satisfactorily 

 answered. 



5. The period of gestation being between fifteen and seventeen days, is in this 

 respect shorter than that of any other known species (tluit of the Kangaroo being 

 thirty-eight days), suggests the idea of the probability of some modification of 

 uterine structure, approaching in some respects that of the birds and ovo- 

 viviparous reptiles. 



G. Although the period of gestation is so short, the young are far more per- 

 fectly developed at birth than has been usually supposed. The views of Blu- 

 rnenbach, who likens them to abortions, as well as those of Dr. Barton, 

 (I quote from Griffith as I have not recently seen the original) appear 

 in this particular surprisingly inaccurate. "The Didelphes," he says, "put 

 forth, not fcetuses, but gelatinous bodies ; they weigh at their first appear- 

 ance generally about a grain, some a little more, and seven of them together 

 weighed ten grains." My observations have convinced me that they are far from 

 being merely "gelatinous bodies," but that they are pretty well developed, 

 indeed nearly as much so as the young of the white-footed mouse and several 

 other species of Rodentia. They are covered by one integument — nourished by 

 the mammse — breathe through nostrils— are remarkably tenacious of life, and 

 are capable of a progressive movement at the moment of their birth. Hence I 

 am not fully satisfied with the accuracy of the terms used by De Blainville nnd 

 Dr. Barton — when they speak of two sorts of gestation — one uterine and the other 

 mammary. It is admitted that for so large an animal as the adult opossum, the 

 young are not only very small, but feeble, and are for several weeks sustained in 

 a kind of secondary domicil, termed the pouch, where they receive warmth, and 

 that they continue during this period firmly attached to the teats, which they do 

 not relinquish till they are pretty well grown. It will be recollected, however, 

 that there is in several of our animals an approach to this latter peculiarity. 

 The white-footed mouse (Mus Icucopus); the Florida rat (Neotoma Floridana), 

 and several species of Bats are known, the two former to travel, and the latter 

 to fly about for one or two weeks, with their young attached to their teats, and 

 that these young are not only blind and naked, but nearlj-^ as helpless as those of 

 the opossum. It will be farther recollected that there are several species in 



