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In some animals, an egg is the zygote, resulting from fertilization of the ovum. It nourishes and protects the embryo. Oviparous animals are animals that lay eggs, with little or no other development within the mother. This is the reproductive way of many fish, amphibians and reptiles, all birds, the monotremes mammals, and most insects and arachnids.
Reptile eggs, bird eggs, and monotreme eggs are surrounded by a protective shell, either flexible or inflexible.
The study or collecting of eggs, in particular bird eggs, is called oology.
The 1.5 kg Ostrich egg is the largest existing single cell currently known, though the extinct Aepyornis and some dinosaurSaurischia Ornithischia The dinosaurs were a diverse and long-lived superorder of prehistoric reptiles. What is a dinosaur? Definition Dinosaurs are a superorder of reptiles that first appeared approximately 230 million years ago. A few lines of primitives had larger eggs. The Bee HummingbirdThe Bee Hummingbird Mellisuga helenae is a hummingbird, and possibly the smallest of all birds. It can be found in Cuba (where it is called the zunzun and the Island of Pines. It weighs approximately 1. External link . produces the smallest known bird egg, which weighs half of a gram. The eggs laid by some reptiles and most fish are even smaller, and those of insects and other invertebrateInvertebrate is a term coined by Chevalier de Lamarck to describe any animal without a backbone or vertebra, like insects, squids and worms. He divided them into two groups, the Insecta and the Vermes. However, the invertebrates are not a coherent group os are much smaller still.
After fertilization, the bird egg is laid by the female and is incubated for a while; then a single young hatches from each egg. Eggs are usually incubated by the female. In some species, such as the Whooping CraneWhooping Crane Scientific Classification : Animalia : Chordata : Aves : Gruiformes : Gruidae Grus americana Binomial name Grus americana ( Linnaeus, 1758) The Whooping Crane Grus americana is a very large crane. This is the tallest North American bird., both the male and the female take turns incubating the egg. The CassowaryCasuarius casuarius ''Casuarius unappendiculatus ''Casuarius bennetti Cassowaries ( genus Casuarius are very large flightless birds native to the tropical forests of New Guinea and Australia. Some nearby islands also have small cassowary populations: it i's eggs, however, are incubated only by the male.
Different animals produce different colored eggs. The pigments protoporphyrin, biliverdin, and zinc chelate of biliverdin, are responsible for the diversity of egg color. These pigments are secreted by cells in the oviductIn oviparous animals (those that lay eggs), the passage from the ovaries to the outside of the body is known as the oviduct . The eggs travel along the oviduct. In mammals, which evolved from reptiles, the oviduct turned into the Fallopian tubes, the uter wall, and can cause speckles if color is added right before the egg is laid. The eggs of modern reptiles are all white, and it is thought that this was true for all animals long ago.
The eggs of cavity nesting birds such as the woodpecker and the kingfisher, are often bright white, making it easy for the parent to locate them.
In species such as the Common GuillemotCommon Guillemot : Animalia : Chordata : Aves : Charadriiformes : Alcidae : Uria : aalge Binomial name ''Uria aalge ( Pontopiddan, 1763) The Common Guillemot known as the Common Murre in North America, Uria aalge is a large alcid. Adult birds are black on, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own egg.