352 FacU, Observations ^ and Conjectures, [Nov. 



The toes of the fore-feet of the new-born embryon opossum 

 are furnished with sharp and hard nails, or claws ; but this 

 is not the case with the hind-feet. The latter are, for some 

 weeks, of little use to the animal ; but hj means of the former it 

 is enabled to cling most firmly to the teat ; and especially to the 

 hair in the marsupium immediately around the teat. 1 cannot 

 suppose, with the respectable Mr. E. Home, of London, that the 

 viscous fluid which surrounds the body of the embryon, when it 

 is first excluded from the uterus, is of any service in faciUtating 

 its attachment to the teat.* 



There is one instance of the evolution of the parts of the 

 embryon-opossum, which has greatly surprised me, and seems, 

 with many other facts, to show, that Nature will, for a long time 

 at least, confound our endeavours to unravel her rete mirabile of 

 final causes. In an embryon-opossum, weighing only sixty or 

 eighty grains, and entirely destitute of the senses of sight and 

 hearing, you may observe, with the naked eye, the marsupium of 

 the female distinctly formed, and even count the number of the 

 teats. 



The humane and ingenious conjecture of Buffon, concerning the 

 preservation of human embryons, or at least fetus, far from being 

 arrived at their last stage of growth, has received some confirm- 

 ation from my experiments : t but I cannot at present detail 

 these experiments. I shall only observe, that an opossura- 

 embryon, or fetus, which weighed sixty-seven grains, hved 

 upwards of thirty hours after I had detached it from the teat. 

 Another, which weighed 116 grains, lived thirty-eight hours, at 

 which time I killed it, by putting it into spirits. 



At the end of about fifty or fifty-two days, from its first recep- 

 tion into the pouch (the period varies somewhat, even among 

 the different individuals of the same birth), the eyes of the young 

 begin to open. At this period, and for a short time before, it is 

 capable of retaking the teat, after having been separated from it 

 by the hand, or otherwise. 



The growth of the young opossum while in the marsupium, 

 and under the immediate care of its mother, is pretty rapid. I 

 have found that the same embryon has increased in weight 531 

 grains in sixty days ; that is, at the rate of almost nine grains 



• Speaking of the kanguroo, Mr. Home says, " It would seem probable, that the 

 mouth of the foetus is originally attached to die nipple by means of the gelatinous 

 substance contained in the uterus." — (Observations on the Mode of Generation of the 

 kanguroo.) 



•f- *' Personne n'a observe la duree de la gestation de ces animaux, que nous presu- 

 mons etre beau coup plus courte que dans les autres ; et comme c'est un exemple singu- 

 lier dans la Nature que cette exclusion prccoce, nous exhortons ceux qui sont a portee 

 de voir des sarigues vivansdans leur pays natal, de tachcr de savoir combien les femeDes 

 portent de temps, et combien de temps encore apres la naissancc les petits restent 

 attaches a la mamelle avant que de s'en separer ; cctte observation^ cnriense par elle- 

 mime^ pourroit devenir utxle^ en nous indiquant pcut-ttre quclque moycn de conserver 

 la vie aux enfans venui avant Ic terme,^* — (Histoire Naturelle, &c. torn. xxi. ?• HI, 

 172. A Fans, 1765. 



