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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]
Oviparous animals laying eggs with thick calcium shells, such as chickens, or thick leathery shells generally reproduce via internal fertilisation so that the sperm fertilises the egg without having to pass through the thick, protective, tertiary layer of the egg. Ovoviviparous and viviparous animals also use internal fertilisation.
Eggs of various birds, a reptile, various cartilaginous fish, a cuttlefish and various butterflies and moths. (Click on image for key) Diagram of a fertilized chicken egg in its ninth day. Membranes: allantois, chorion, amnion, and vitellus/yolk. Six commercial chicken eggs — view from the top against a white background
Cock: a fertile adult male chicken [6] [7] Cockerel: a young male chicken [8] Hen: an adult female chicken [9] Pullet: a young female chicken less than a year old. [10] In the poultry industry, a pullet is a sexually immature chicken less than 22 weeks of age. [11] Rooster: a fertile adult male chicken
This chicken egg has been soaked in vinegar for a few days and has become translucent and flexible. Anatomy of a chicken egg. The bird egg is a fertilized gamete (or, in the case of some birds, such as chickens, possibly unfertilized) located on the yolk surface and surrounded by albumen , or egg white.
They hold the eggs internally for several weeks, providing nutrients, and then lay them and cover them like birds. Like marsupial " joeys ", monotreme " puggles " are larval and fetus-like, [ 9 ] as like them they cannot expand their torso due to the presence of epipubic bones, forcing them to produce undeveloped young.
Some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift or sink in the water column. Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring.
The yolk of a chicken egg Diagram of a fish egg; the yolk is the area which is marked 'C'. Among animals which produce eggs, the yolk (/ ˈ j oʊ k /; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo.