Abstract
The period between copulation and birth in Setonix brachyurus Quoy and
Gaimard is about 27 days. Approximately 1 day elapses between copulation
and fertilization. The gestation period is slightly less than the length of one
oestrous cycle.
The tuba1 journey of the fertilized egg occupies only about 1 day. The
unilaminar blastocyst 3-4 days after mating, with its enclosing membranes,
measures about 0.3 mm diameter. At this stage the corpus luteum is not fully
developed and a luteal phase is not evident in the uteri. Bilaminar blastocysts
and later embryonic stages are associated with a well-developed corpus luteum
and luteal changes in the uteri. Towards the end of pregnancy the corpus
luteum shows degenerative changes and ovaries and uteri exhibit evidence of
approaching oestrus. The allantois of the uterine embryo does not form a
placental structure. A well-developed, vascular, trilaminar yolk-sac placenta
occurs during the later stages of embryonic life.
Oestrus and ovulation occur shortly after the female gives birth. The
corpus luteum formed following post-partum ovulation remains of small size
and functions during lactation of the young in the pouch as the corpus luteum
of lactation. Luteal changes do not occur in the uterus during this time and a
lactation anoestrus takes place. Removal of the young from the pouch causes
growth of the corpus luteum of lactation and the onset of luteal changes in the
uterus.
If fertilization takes place at post-partum oestrus the resulting embryo
remains as an unimplanted blastocyst of small size during the time the pouch
is occupied by a suckling foetus. This quiescent embryonic stage will proceed
to normal development following removal of the young from the pouch.
Blastocysts may remain unimplanted for up to 5 months.
The probable significance of the gestation period in relationship to the
length of the oestrous cycle and the placental structure is discussed. The
ovulation-inhibiting function of the corpus luteum of lactation and its later
luteal function are compared. The mechanism of delayed pregnancy in
Setonix is discussed and comparisons are made with known cases of delayed
birth in other mammals. Some concluding remarks are made on the breeding
habits of Setonix in relation to its environment.
Subject
Animal Science and Zoology,Ecology, Evolution, Behavior and Systematics
Cited by
62 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献