Search results
Results from the WOW.Com Content Network
The egg cell is generally asymmetric, having an animal pole (future ectoderm).It is covered with protective envelopes, with different layers. The first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane (zona pellucida in mammals).
Most mammals develop similarly to humans; during the earliest stages of development, the embryo is largely indistinguishable from another mammal. However, there are phenomena found in human beings not found in all other mammals, as well as phenomena occurring in other mammals, but not in humans.
Male mammals ejaculate semen through the penis into the female reproductive tract during copulation. [28] [29] Ejaculation usually occurs after only one intromission in humans, canids, and ungulates, but occurs after multiple intromissions in most mammal species. [30] [31] Copulation can induce ovulation in mammal species that do not ovulate ...
Citing reptiles and other animals with a much slower biological aging process than mammals, de Magalhães hypothesizes that during the Mesozoic Era, mammals either lost or deactivated genes ...
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 ...
Species that use a breeding season usually give birth during a specific time of year when food is available. [2] Various other factors can come into play in determining the duration of gestation. For humans, male fetuses normally gestate several days longer than females and multiple pregnancies gestate for a shorter period. [2]
There is an extensive variation in the type of trophoblast cells, and structures of the placenta across the different species of mammals. [8] Of the five recognised stages of implantation including two pre-implantation stages that precede placentation , the first four are similar across the species.
Sacrococcygeal teratomas, tumours formed from different types of tissue, that can form, are thought to be related to primitive streak remnants, which ordinarily disappear. [ 10 ] [ 11 ] [ 13 ] First arch syndromes are congenital disorders of facial deformities, caused by the failure of neural crest cells to migrate to the first pharyngeal arch.