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Diagram of stages of embryo development to a larval and adult stage. In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm cell (spermatozoon). [1]
The only living mammals that lay eggs are echidnas and platypuses. In the latter, the eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally). [11] After laying her eggs, the female curls around them.
In the United States alone, more than 8 billion chickens are slaughtered each year for meat, [78] and more than 300 million chickens are reared for egg production. [79] The vast majority of poultry is raised in factory farms. According to the Worldwatch Institute, 74% of the world's poultry meat and 68% of eggs are produced this way. [80]
Hamburger and Hamilton aimed to provide a detailed description of developmental events, modeled on an earlier system for Axolotl by Harrison. The Hamburger–Hamilton system provides advantages over the Carnegie system in that it allows the developing chick to be accurately characterized during all embryonic stages, and is used universally in ...
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Voting period is over. Please don't add any new votes. Voting period ends on 10 Jun 2017 at 01:47:55 (UTC). Original – Diagram of a chicken egg in its ninth day of incubation showing all four extraembryonic membranes along with the embryo, the air pocket, and the shell
The mammalian male reproductive system contains two main divisions, the penis and the testicles, the latter of which are where sperm are produced and usually held in a scrotum. [5] In humans, both of these organs are outside the abdominal cavity , but they can be primarily housed within the abdomen in other animals.
The chicken embryo is a unique model that overcomes many limitations to studying the biology of cancer in vivo. The chorioallantoic membrane (CAM), a well-vascularized extra-embryonic tissue located underneath the eggshell, has a successful history as a biological platform for the molecular analysis of cancer including viral oncogenesis, [8] carcinogenesis, [9] tumor xenografting, [1] [10] [11 ...