46 ■ ' [April, 



snpialia, a modified structure in these parts; and the allantols, umbilical cord, 

 as well as the omphalo-mcsenteric arteries and veins may exist in the absence of 

 a placenta. In the very unsatisfactory examinations I have been enabled to make 

 on this subject, I came to the conclusion that there was some reason to believe 

 that an allantois existed, and that there were some traces of the omphalo- 

 mesenteric vessels running through the mucolis substance in which the young lay 

 imbedded. It is proper, however, to observe, that my friends Prof. Hume and 

 Drs. Harlbeck and Michel, who subsequently examined the well preserved spe- 

 cimen of the 15th, and the imperfect remains of the contents of the other uteri, 

 came to the very opposite conclusion. I nevertheless hazard the conjecture that 

 these appendages may yet be found in the uterus at an advanced stage of preg- 

 nancy. This suspicion, however, remains either lo be confirmed or refuted by a 

 more favourable opportunity for examination. Owen, in describing, in 1834, the 

 foetus and membranes of the Kangaroo at apparently the middle period of uterine 

 gestation, found its condition such as obtains in the viper and other ovo- 

 viviparous reptiles, there being no trace of the existence of an allantois In 

 1837, however (see Magazine of Nat. Hist., p. 481), having received another 

 specimen in a more advanced stage, he found numerous ramifications of the um- 

 bilical vessels constituting a true allantois. The umbilical cord extended three 

 lines from the abdominal surface of the foetus. Having seen and examined that 

 specimen, I may have unconsciously formed a theory which has misled me in 

 conjecturing that I had observed a similar organization in the opossum. 



Letter from MiJdleton Michel,, M. D., of Charleston, S. C. 



To tlie Rev. .Tuhn Baclinian, U. D. 



Dear Du. — You will oblige me by adding the few facts which I am able to 

 state, concerning the habits and generation of our Opossums, to your valuable 

 communication, addressed to the Philadelphia Academy of Natural f^ciences. 



1st. I have first noticed their mode of copulation, which, though singular in 

 itself, finds its explanation in the position and structure of the penis. The female, 

 after repeated solicitations on the part of the male, which are conducted as among 

 other animals, finally reclines upon her left side, beijig drawn into this position 

 by the male ; his front legs are employed in securing her, while the hinder ones 

 are made to pass on each side of the loins of the female, over and between htr 

 hind legs. The penis, measuring two inches and more, is thus brought into more 

 immediate relation with the sexual organs of the female. Copulation lasted five 

 minutes. The sperm passes along the lateral canals, its only possible course, as 

 the bifurcated organ of intromission is received to some distance into them. 



2d. I have further determined, that the period of gestation is not twenty and 

 twenty two davs as has been believed I placed a female with the male on the 

 27th of January, and on the 2Sth, at 7| o'clock, A. M., I witnessed them en- 

 gaged in the act. She was left three days with the male, then isolated, and on 

 the 12th of February, fifteen days after the first coitus, had her young, six in 

 number, in the pouch. Admitting that the period may vary from fifteen to 

 seventeen days, the having settled this point I regard of pai amount importance 

 in answer to another question to be presently examined. 



3d. The rut begins in January and continues till June, as I have seen ynuiin 

 just received into the pouch during these months. 



