Their gestation period is shorter and varies from 25 days in the mouse to 31 days in rabbits and days in the gorilla. For example the shortening day length in autumn will bring sheep and cows into season so the foetus can gestate through the winter and be born in spring. The external opening of the female genitalia is called the vulva.
This is a blastocyst see diagram These signs are turned off again at the end of the oestrous cycle. File:Anatomy and physiology of animals Diagram summarizing the functions of the male reproductive organs.
Blood and tissues from the inner lining of the uterus combine to form the menstrual flow, which in most girls lasts from 3 to 5 days. The zygote then starts to divide by mitosis see Chapter 3 to form a new animal with all its body cells containing chromosomes that are identical to those of the original zygote see diagram The mature follicle consists of outer cells that provide nourishment.
File:Anatomy and physiology of animals Fetus and placenta.
Only a few animals breed throughout the year. Sperm are made up of three parts: a head consisting mainly of the nucleus, a midpiece containing many mitochondria to provide the energy and a tail that provides propulsion see diagram However, most birds make do with a small amount of erectile tissue known as a papilla.
To easily explain how the egg cells work, we can take the menstrual cycle as an example. After it has separated from the inner lining of the uterus, contractions of the uterus push it out, along with its membranes and fluids.
Chorionic gonadotrophin is another hormone secreted by the placenta and placental membranes. Toward the end of puberty, girls begin to release eggs as part of a monthly period called the menstrual cycle. Can't recover, please submit a ticket. Salmonella infections usually resolve in days and often do not require treatment unless the patient becomes severely dehydrated or the infection spreads from the intestines.
They then develop to quite an advanced stage inside the body of the female. Male birds have testes and sperm ducts and male swans, ducks, geese and ostriches have a penis.