MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 343 



riiiieiits on an Opossum {D'ldelphys Azarce, Temm.) of about the same size, in which 

 the uterine gestation lasted twenty-five days. 



In the Kangaroo (^Macropus major, Shaw,) uterine gestation continues thirty-nine 

 days, which seems still more remarkable for its shortness, if we consider the difference 

 in the size of the Opossum and Kangaroo. A longer period has, indeed, been stated 

 to elapse between the impregnation and parturition of the latter animal ; but the pre- 

 cautions taken to ensure accuracy in the observations which led to the determination of 

 the period of thirty-nine days were such as to admit of no source of error ; and the size 

 of the mammary foetus figured by Sir Everard Home in the 85th volume of the Philo- 

 sophical Transactions could hardly be reconciled with the duration of four months 

 assigned to uterine gestation in the Kangaroo by Professor Geoffroy St. Hilaire *. 



The period of gestation was determined in a female Kangaroo in the Menagerie of 

 the Zoological Society. She was placed with the male only at such times as they could 

 be watched. She had a young one of the previous year, which had quitted the pouch, 

 but was still sucking occasionally. The coitus was observed on the 27th August 1833, 

 at 1 P.M. ; and as it was known that she could not have had intercourse with the male 

 for three months prior to this date, that fact, and the size of the young one when she 

 was selected for the experiment, left no doubt of her being unimpregnated until the date 

 above mentioned. She was separated from the male the same day, and was kept apart 

 in a separate shed and paddock until parturition took place. And here I must ex- 

 press my great obligations to the Council of the Zoological Society for the permission 

 given me to conduct my experiments under circumstances so favourable as are 

 afforded in their noble Vivarium : every arrangement in the building appropriated to 

 the kangaroos which could facilitate my observations on them was promptly effected, 

 and the services of an intelligent keeper were allotted to me. 



In order to inure the female to the examinations of the pouch when they should 

 become indispensable, they were commenced six days after the copulation, and were 

 repeated every morning and evening until the 5th October, when, at 7 a.m., the 

 foetus was discovered in the pouch attached to the left superior nipple. On the pre- 

 ceding day, at the same hour, a greater quantity of the moist brown secretion peculiar 

 to the pouch was noticed, indicating a commencing determination of blood to that 

 part ; and at different periods during the day the female was observed to put her head 

 into the pouch and lick off the secretion. When she was again examined at six 

 o'clock in the evening, a slight increase of the secretion was the only perceptible 

 change in the state of the pouch ; but there was no appearance in the nipples indica- 

 tive of the event so soon about to take place. 



The nipple in use by the young one of the previous year was the right superior, or 

 anterior one : it was nearly two inches in length, and one third of an inch in diame- 

 ter, while the other three were about half an inch in length, and about a line in dia- 

 meter. I took notes of the appearance of the marsupium on the 6th, the 10th, 15th, 



* Annales des Sciences Naturelles, torn. ix. p. 340. 

 2 y2 



