M. de Saint-Hilaire on Didelphis Virginiana. 405 



At length however, the foetuses which I possess, through the 

 generosity of M. Turpin, have demonstrated that these facts have 

 been incorrectly given ; I have observed in them evident vestiges 

 of placental organization, and of an umbilicus. But it was 

 necessary to go farther, and ascend by observation nearer to the 

 origin of those organic formations, in order to discover the first 

 elements of the constitution which characterises the mammifera. 



The researches which gave rise to the preceding remarks were 

 all directed to animals already received into the pouch ; but if 

 more reflection had been bestowed on the subject, the surprise, 

 occasioned by the appearances of their developeraent would have 

 been much diminished : for could these animals produce in this 

 supplemental pouch, this second domicile, as Barton calls it, au 

 organization, which in truth, is only compatible with all the de- 

 pendencies of the first? A placenta, an umbilical cord, and en- 

 veloping membranes, belong to the foetus in the aduterum, one of 

 the parts of the sexual canal. These would be observed in a foetus 

 in that pouch, or the first domicile ; but no one has hitherto pro- 

 cured us this observation. Barton attempted it without success, 

 evidently for want of perseverance. He was afraid of sacrificing 

 individuals which he never possessed in sufficient number to sub- 

 mit them to multiplied experiments. 



However it may be, two young males of the foetuses presented 

 to me by M. Turpin, have evidently a large umbilical aperture, 

 large, I mean, in comparison with their very small size. I say 

 the two males, and not the third individual, which was a female, 

 lest it should be thought that I mistook the entrance into the pouch 

 for the vestige of an umbilicus. There is both the vestige of an 

 umbilicus, and a scrotum below it, in the males. 



Thus, by this observation we return to the common course of 

 the mammifera ; for we see, at the commencement of the forma- 

 tion, all the essential parts, on which, in a more advanced stage, 

 will depend the characteristic distinctions of the mammifera. 

 The same series of transformations occurs in all these animals, 

 ovulum, embryo, and foetus. These three states of genital pro- 

 ducts require three distinct situations, which, in the normal mam- 

 mifera, are found within the sexual canal ; but in the marsupial 



