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Embryonic diapause [a] (delayed implantation in mammals) is a reproductive strategy used by a number of animal species across different biological classes.In more than 130 types of mammals where this takes place, the process occurs at the blastocyst stage of embryonic development, [1] and is characterized by a dramatic reduction or complete cessation of mitotic activity, arresting most often ...
Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization. The fertilized egg cell is known as the zygote. [2] [5] To prevent more than one sperm fertilizing the egg , fast block and slow block to polyspermy are used. Fast block, the membrane ...
Diapause may occur in a completely immobile stage, such as the pupae and eggs, or it may occur in very active stages that undergo extensive migrations, such as the adult monarch butterfly, Danaus plexippus. In cases where the insect remains active, feeding is reduced and reproductive development is slowed or halted.
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Due to the fact that placental mammals and marsupials nourish their developing embryos via the placenta, the ovum in these species does not contain significant amounts of yolk, and the yolk sac in the embryo is relatively small in size, in comparison with both the size of the embryo itself and the size of yolk sac in embryos of comparable developmental age from lower chordates.
A female dog is usually diestrous (goes into heat typically twice per year), although some breeds typically have one or three cycles per year. The proestrus is relatively long at 5 to 9 days, while the estrus may last 4 to 13 days, with a diestrus of 60 days followed by about 90 to 150 days of anestrus.
Canine sperm can live for 10 to 11 days [22] in the oviducts (fallopian tubes) so if a female is bred 10 days before the oocytes (eggs) can be fertilized, she will appear to have a gestation length of 70 days. If she is bred on the day the oocytes can be fertilized, her gestation length will appear to be 60 days long.
The theoretical issue of male ectopic pregnancy (pregnancy outside the uterine cavity) by surgical implantation has been addressed by experts in the field of fertility medicine, who stress that the concept of ectopic implantation, while theoretically plausible, has never been attempted and would be difficult to justify – even for a woman ...