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G. DALE BUCHANAN

Summary.

Implantation did not occur at the usual time in rats ovariectomized on Days 1,2,3 or 4 post coitum (p.c.), but could be induced subsequently by injections of progesterone and oestrone, begun in some instances as late as Days 12, 14, 18 and 8 p.c., respectively. Normal numbers of implantation sites were found in most animals when injections were begun on or before Day 8 p.c. Thereafter, the number of rats with implantation sites and the number of sites observed in each rat declined. The interval after ovariectomy during which blastocysts were recovered from rats not receiving hormones corresponded with the period when implantation could be induced, suggesting that blastocysts remained viable for as long as they survived.

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G. DALE BUCHANAN

Summary.

A nine-banded armadillo was found to contain an early implantation site in the fundic tip of the uterus and an extraordinarily large free blastocyst in the central portion of the uterine cavity. This finding suggests that only the small portion of the endometrium in the fundic tip of the uterine cavity is competent to accept the blastocyst.

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G. DALE BUCHANAN

Summary.

Bilateral ovariectomy before Day 10 post coitum (p.c.) prevented implantation of ferret blastocysts. However, blastocysts survived for about a week beyond the normal time of implantation and although the zonae pellucidae were not shed, many underwent a marked increase in size similar to that seen in normal blastocysts at the time of implantation. Implantation occurred when ovariectomy was performed on Day 10 p.c., but resorption followed immediately.

Immediate regressive changes were seen in uterine cornua of animals ovariectomized on Day 4 p.c. When ovariectomy was performed later, there was continued histological differentiation of the endometrium and some cornual growth. Cornua from animals ovariectomized on Day 6 p.c. were smaller than normal but were histologically similar to cornua from intact animals until about Day 20 p.c., after which regressive changes were found. Cornua from animals ovariectomized on Days 8 and 10 p.c. showed definite, albeit subnormal, growth in size after ovariectomy but exhibited essentially the same degree of histological development as normal cornua until Day 25 p.c.

It is suggested that the ferret uterus, once stimulated by ovarian hormones, is capable of prolonged response without further stimulus.