404 M. de Saint-Hilaire on Didelphis Virginiana. 



them from their mother, very soon after their introduction into 

 the pouch. The size of these little animals, was rather more than 

 five lines (^*^ inch French), from the extremity of the nose to the 

 insertion of the tail. 



These foetuses were already formed, which leads me to think 

 that Dr. Barton is mistaken, as to the moment of their entering 

 the pouch. I have attentively observed, and even dissected these 

 very small animals, and moreover, I have had magnified drawings 

 made of them six times the natural size. What I have learnt by 

 studying these preparations will add much to the facts which I 

 have already stated respecting the developement of marsupial 

 embryos. Sir Everard Home, in 1795, in treating of the sexual 

 organs of the Kangaroos, announced an unusual circumstance, 

 and desciibed a foetus without the umbilical cord : Barton heard 

 of it, and hastened to verify so extraordinary a fact, and found 

 it correct as far as regards the foetus of his Didelphes. M. de 

 Blainville reverted to these results, and announced (Bulletin des 

 Sciences, 1818, p. 24,) " that he had been unable, notwith- 

 standing the utmost care, to discover in the foetuses of marsupial 

 animals, either vein, umbilical artery, urinary passage, (oura- 

 que) suspensor-liganient of the liver, or thymus." 



In short, here are animals constituted like the mammifera, and 

 which are true mammifera, and yet present such anomalies ! 

 They do not begin, but they end in being mammifera I It is true 

 I quoted these observations, made before my own, but still I 

 thought I perceived, not without' regret, a sort of contradiction in 

 them. For it was in some measure a misunderstanding of the 

 spirit of organic developement. Every generation is necessarily 

 established in a successive order : the first produced organs en- 

 gender those to come, for they contain the germ of those which 

 are to appear afterwards. Good sense alone would have boldly 

 asserted that the cause of the existence of the second was visibly 

 written in the existence of the first. 



These objections dwelt upon my mind ; but what are argu- 

 ments opposed to facts ? I submitted, and I adhered to the facts, 

 without troubling myself any further with logical rules which 

 tended to lead me away from them. 



