We are unhappy at not being able to transmit you as regular accounts from Monticello as you are desirous of having. The discontinuance of the post throws us entirely on the Waggons for the conveyance of our letters, a method not only irregular but extremely uncertain. It is particularly painful to us to be frequently in doubt from the same cause about the state of your health as there is nothing in which we are so much interested. Your letter of the 17th. March reached Monticello on the 19th of April and we often receive 2 or 3 packets at once. A sure opportunity by means of Bob who goes to Fredericksburg on a visit to his wife, induces us all to write at the same time.

I am sorry to let you know that I have little hopes of arriving at any thing absolutely conclusive this year, on the question concerning the Opossum. Being unluckily misinformed with respect to the time of the appearance of the young in the false pouch I was not extremely anxious to procure subjects till the first weeks of March had elapsed. Of four which I have examined one was in no way pregnant, the young of the other 3 were hanging at the teats in the false pouch, but were much larger, even those of the smallest brood, than a pea or a bean of which size it is said they have been seen in the same situation. The first had been taken in the middle of Winter before it had intercourse with the male and was kept alive till the beginning of April: the teats had the usual appearance of those of barren animals but the false pouch was as complete in every respect as in the other subjects. From this it appears that Mr. Rittenhouse was misinformed. The young opossums kept themselves at the teat by pressing the extremity of it between the tongue and the end of the upper jaw: an attempt to separate them from it by drawing them forcibly away would have occasioned a considerable laceration, it was evident; but by opening the mouth gently with the end of a pin they were removed without the smallest marks of violence, altho the most particular attention was bestowed. From the most accurate observation of 10, which was the number of the youngest brood, no connecting membrane could be discovered. The little animals of that brood even when removed in this manner from the false pouch, if placed near it, easily found their way in again; yet they appear to be as imperfect as the fetus in the larger Quadrupedes a considerable time before its birth. Several of them are preserved in Spirits to be submited to your inspection.—The internal organs of generation in the Opossum are perfect in every respect. The Uterus Tyson I think, has remarked to have two cavities: these cavities however communicate with each other at some distance from the neck. Since my dissection it has occurred to me that there might be a passage from some part of the Vagina to the false belly and this shall be one of the chief objects of my next enquiry. I recollected Mr. Madisons idea of a communication between the Uterus directly and the false belly but am convinced that there is no such passage. A way leading from some part of the Vagina is much more probable. The end at which my dissections immediately aimed was the discovery of a gravid Uterus, as that would have afforded decisive proof in favor of the Opinion of several European Naturalists (vid. Bonnet Contemplation de la Nature V.3. p.45. note) viz. that the time of gestation is extremely short with the Opossum and that parturition is with it a kind of natural Abortion.

I shall have it in my power soon to give you a more minute and particular account of my observations with any thing new which may occur.

I am sorry not to be able to give you a good account of the Diary you desired me to keep. I could only find one Thermometer in Richmond for Sale which was short, badly graduated and at an exorbitant price. I send you observations during the present month made with the old Spirit of Wine Thermometer in the Study.

Colub. Parus—. Pl. Chionanthus Virg. Cypripedium Calc. Crataegus Crus ga Morus Rubra. Hyacin. comosus. Aquilegia Canad. Prunus Virg. Magnolia 3 pet. &c. between 18 and 30. The Chasm is occasioned by a trip to Varina. I have only noted the birds and a few plants, such of either only as appeared on the top of the Mountain. Dear Sir your most aff. & obed. Servt.