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The intact white shell of a chicken egg.

The term eggshell is a term for the outer covering of a hard-shelled egg, and some forms of eggs with soft outer coats. Image File history File links Question_book-3. ... Image File history File linksMetadata Size of this preview: 600 × 599 pixel Image in higher resolution (625 × 624 pixel, file size: 109 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Egg (food) Eggshell... Image File history File linksMetadata Size of this preview: 600 × 599 pixel Image in higher resolution (625 × 624 pixel, file size: 109 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Egg (food) Eggshell... In most birds and reptiles, an egg (Latin ovum) is the zygote, resulting from fertilization of the ovum. ...

The generalized eggshell structure, which varies widely among species, is a protein matrix lined with mineral crystals, usually of a calcium compound such as calcium carbonate. It is calcium build-up and is not made of cells. Harder eggs are more mineralized than softer eggs. A representation of the 3D structure of myoglobin showing coloured alpha helices. ... For other uses, see Calcium (disambiguation). ... Calcium carbonate is a chemical compound, with the chemical formula CaCO3. ...

Diversity

Insect eggs

Insects and other arthropods lay a variety of styles and shapes of eggs. Some have gelatinous or skin-like coverings, others have hard eggshells. Softer shells are mostly protein. It may be fibrous or quite liquid. Some arthropod eggs do not actually have shells, rather, their outer covering is actually the outermost extraembryonic membrane, the chorion, which serves to protect inner layers. The chorion itself can be a complex structure, and it may have different layers within it. It may have an outermost layer called an exochorion. Eggs which must survive in dry conditions usually have hard eggshells, made mostly of dehydrated or mineralized proteins with pore systems to allow respiration. Arthropod eggs can have extensive ornamentation on their outer surfaces. Orders Subclass Apterygota Archaeognatha (bristletails) Thysanura (silverfish) Subclass Pterygota Infraclass Paleoptera (Probably paraphyletic) Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Infraclass Neoptera Superorder Exopterygota Grylloblattodea (ice-crawlers) Mantophasmatodea (gladiators) Plecoptera (stoneflies) Embioptera (webspinners) Zoraptera (angel insects) Dermaptera (earwigs) Orthoptera (grasshoppers, etc) Phasmatodea (stick insects) Blattodea (cockroaches) Isoptera (termites) Mantodea (mantids) Psocoptera... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... In animal physiology, respiration is the transport of oxygen from the ambient air to the tissue cells and the transport of carbon dioxide in the opposite direction. ...

Fish, amphibian and reptile eggs

Fish and amphibians generally lay eggs which are surrounded by the extraembryonic membranes but do not develop a shell, hard or soft, around these membranes. Some fish and amphibian eggs have thick, leathery coats, especially if they must withstand physical force or desiccation. For other uses, see Fish (disambiguation). ... For other uses, see Amphibian (disambiguation). ...

While many reptiles lay eggs with flexible, calcified, eggshells, there are some that lay hard eggs. Eggs laid by snakes generally have leathery shells which often adhere to one another. Depending on the species, turtles and tortoises lay hard or soft eggs. Several species lay eggs which are nearly indistinguishable from bird eggs. Hatching reptiles, like most birds, have egg-teeth with which they slit or peck an opening into the shell to help them emerge. Reptilia redirects here. ... An egg tooth is not a true tooth, but a small horny protruberance on the beak or nose of vertebrates that are hatched from eggs, ie: birds and reptiles. ...

Bird eggs

Birds are known for their hard-shelled eggs. The eggshell is approximately 95% calcium carbonate crystals, which are stabilized by a protein matrix. Without the protein, the crystal structure would be too brittle to keep its form. The standard bird eggshell is a semipermeable membrane filled with thousands of pores and covered on its outer surface with a cuticle (called the bloom if it is around a chicken egg), which helps the egg retain its water and keep out bacteria. As an egg develops within a bird's reproductive system, the shell is laid down as a liquid mineral layer around the already-formed extraembryonic membranes. This takes place in a part of the bird's oviduct which is called the uterus and serves a very different purpose from the uterus of a mammal. The shell is laid down by shell glands. In an average laying hen, the process of shell formation takes around 20 hours. Pigmentation is added to the shell, coloring it any of a variety of colors and patterns depending on species. The waxy cuticle is deposited on the shell in the vagina of the bird's oviduct. The chick has an egg-tooth which it uses to start a hole in the hard eggshell to allow it to hatch. For other uses, see Bird (disambiguation). ... Calcium carbonate is a chemical compound, with the chemical formula CaCO3. ... Scheme of semipermeable membrane during hemodialysis, where red is blood, blue is the dialysing fluid, and yellow is the membrane. ... Eponychium is the anatomical term for the human cuticle In biology, the term cuticle or cuticula is given to to a variety of tough but flexible, non-mineral outer coverings of an organism, or part of an organism, that provide prtoection. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... In oviparous animals (those that lay eggs), the passage from the ovaries to the outside of the body is known as the oviduct. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including milk producing sweat glands, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex... This article or section does not adequately cite its references or sources. ... Natural Ultramarine pigment in powdered form. ... An egg tooth is not a true tooth, but a small horny protruberance on the beak or nose of vertebrates that are hatched from eggs, ie: birds and reptiles. ...

Mammal eggs

Monotremes, egg-laying mammals, lay soft-shelled eggs similar to those of reptiles. The shell is deposited on the egg in layers within the uterus. The egg can take up fluids and grow in size during this process, and the final, most rigid layer is not added until the egg is full-size. Families †Kollikodontidae Ornithorhynchidae Tachyglossidae †Steropodontidae Monotremes (monos, single + trema, hole; refers to the cloaca) are mammals that lay eggs instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria). ...

See also

• The Eggshell skull rule, in tort law.