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Female red kangaroos in captivity became sexually mature at 15-20 months and males at about 2 years of age. 'I'he oestrous cycle averaged 34-35 days in length and the gestation period was 33 days. The interval from fertile mating to post-partum oestrus was not significantly different from the length of the oestrous cycle. The oestrous cycle was accompanied by changes in the cell composition of the vaginal smear, by changes in the urogenital sinus and the area surrounding the urogenital opening, and by changes in the pouch and teats. The approach of oestrus could not always be predicted but the immediate post-oestrous condition could always be recognized even if mating had not occurred at oestrus. Pre-mating and mating behaviour is described. Breeding in the red kangaroo in captivity was virtually continuous but there was evidence that some females showed a slightly reduced fecundity in the winter months.The births of 18 young were closely observed. At the approach of parturition most females cleaned away the scale inside their pouches by licking. For parturition females assumed the "birth position" with the back usually supported, the hind legs extended straight forwards, the tail passed forwards between them and the trunk inclined forwards. Females adopted the birth position up to 20 or more times before birth occurred. They licked the urogenital opening before birth occurred but no female licked a path in the fur which the young followed to the pouch. Birth was preceded by the appearance of yolk sac fluid and usually by the embryonic allantois which appeared in the form of a fluid-filled sac. The young were born in the amnion and climbed unaided by the mother up a generally dry route in the fur to the pouch. During the first part of the journey they were attached by the umbilical cord to the ruptured yolk sac which was still in the birth canal. Birth was followed by the appearance of blood, viscous fluid, and the yolk sac all of which were carefully licked up and eaten by the mother. Seventy-six young born in captivity were made up of 42 females, 32 males, and two of unknown sex.All behaviour associated with birth occurred in non-mated females. Non-rnated parous and virgin females which had newborn young transferred to their teats at the appropriate stage after oestrus produced milk and the foster young were reared normally. Growth rates of foster young did not differ significantly from that of control young reared in their mothers' pouches.The teats became evident as raised areas in the pouch at the time of sexual maturity. Only the teat to which the newborn attached produced milk and this one was used by the suckling young, to the exclusion of the other three teats, during the time it was suckled both in and out of the pouch. Pouch cleaning was a frequent activity of females suckling young in the pouch. Young first left the pouch for short periods at the age of about 190 days and the method of re-entering the pouch is described. Females which mated in post-partum oestrus exhibited delayed inplantation and the...

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