J 823.] relative to the Generation of the Opossum. 353 



daily. But, as you may readily imagine, its increment, in bulk 

 and weight, is much greater one day than another. The animal 

 attains to nearly its full growth in about five months ; but never, 

 I beheve (in our latitudes, I mean), procreates the first year of 

 its existence. 



Possibly I have been relating nothing but what is familiarly 

 known to you. The following fact, however, will, I flatter 

 myself, be entirely new to you ; and if the relation of it should 

 give you half the pleasure that the discovery of it did me, I am 

 persuaded, that this letter will not be altogether unacceptable to 

 .you. 



On the 14th of May, I purchased a female opossum, with 

 seven young ones. They were at this time about the size of 

 rats, two-thirds grown ; and subsisted partly upon their mother's 

 milk, and partly upon meats and vegetables. Of course, the 

 period of their necessary connexion with the mother was at an 

 end. 



On the 21st of the month, that is, at the expiration of seven 

 complete days, upon looking into the box which contained the 

 animal, I found that the mother had just excluded from her 

 uterus seven embryons, the smallest of which scarcely weighed, 

 one grain ; another barely two grains ; and the remaining five 

 (taken together) exactly seven grains. 



You, my dear Sir, who are by no means a stranger to the 

 enthusiasm that is inspired by the contemplation and study of 

 Nature, will readily imagine what were my sensations on the 

 discovery of this unexpected new family of didelphides. The 

 fact, which I was so fortunate as to witness, is, in my opinion, 

 one of the most interesting in the whole science of zoology ; and 

 so far as I know, it has never been noticed by any naturalist but 

 myself. 



You will, I doubt not, immediately attach to this fact its pro- 

 per and full value. We are no longer, it appears to me, at a 

 loss to comprehend the final inteqtion of Nature in furnishing 

 the opossum with a pouch for the reception of the tender 

 embryons, excluded, as we have seen they are, from the uterus, 

 in a very unformed state. Nature has determined that the female 

 didelphis shall produce, at least, two litters of young ones, in the 

 course of the same year. Superfetation (I should, perhaps, in 

 strict propriety, say uterine superfetation) is wholly incompatible 

 with the established laws of the economy of the didelphis. But 

 Nature, always provident, wastes no time. While, therefore, 

 the first htter of young opossums are fast approaching to their 

 ' adult or more independent state, the mother accepts the ardour 

 of the male ; she is impregnated; and after a gestation which is 

 not, I think, remarkably short, if we consider the small size of 

 the embryons when they are excluded from the uterus,* the 



* BufFon, in the passage which I have quoted from his work, has very properly 

 observed, that the uterine gestation of Jiis Sarigue is very short : short, indeed, when 



Neiv Series, vol. vi. 2 a . 



