|
Search over 100 encyclopedias and dictionaries: |
Research categories | Follow us on Twitter |
Research categories
View all topics in the newsView all reference sources at Encyclopedia.com |
|||
Egg
EggThe egg, or ovum, is the gamete (reproductive sex cell) produced by most female animals. It is fertilized by the sperm, which is the male gamete. The term "egg" is commonly used to include the acellular structures that surround the ovum. In "higher" animals, including arthropods (such as crabs and insects), most fish, most amphibians, many reptiles (including birds), and some mammals (the echidna and the platypus), the egg is a relatively large structure in which the young matures outside the mother's body. This form of reproduction is called oviparous, or egg-laying. In the viviparous, or live-bearing, form of reproduction used by some fish, amphibians, and reptiles, as well as most mammals, the developing egg remains within the mother's body. The eggs of both amphibians and amniotes (reptiles and mammals) generally contain a protective covering and the cells from which the young develop. The protective covering may take on a number of different forms, depending on the animal. In amphibians the coating is gelatinous and clear. In amniotes, it may be leathery like the egg of a reptile, or hard like the egg of a bird. In live-bearing species of lizards and snakes, the shell is a thin membrane through which materials can easily pass. In most amphibian and amniote eggs of both oviparous or viviparous species, a large yolk mass within the egg nourishes the developing embryo. In some viviparous reptiles and most mammals, nutrition comes directly from the mother through a specialized aggregation of blood vessels. In mammals, this structure is called a placenta. The structure, size, and number of eggs produced depend on the lifestyle and environment of the animal that makes them, and there is a fair amount of variation. There are two general strategies involving the size and number of eggs: the mother's limited energy resources will either go toward making a smaller number of larger offspring or a larger number of smaller offspring. Some species produce many offspring to increase the number that survive in a harsh environment. In this strategy, survival is largely dependent on chance, and many of the young die. Species that invest more energy into a smaller group of larger young increase the chance that each individual will survive, based on the assumption that larger young are stronger than smaller young. Both oviparous and viviparous strategies are represented among amphibians (frogs, salamanders, and the often-hiding, wormlike caecilians). The eggs of oviparous amphibians vary greatly in size. In addition, because the gelatinous membrane that surrounds an amphibian egg is not safe from losing internal fluids, desiccation (drying out) is a serious threat. Most species lay their eggs in or near water, although some salamanders will bury their eggs to keep them moist and cool. Because an amphibian egg is not waterproof, it exchanges fluids and gases easily with the surrounding water. This is critical for supplying the egg with oxygen and for releasing harmful waste products from the confines of the egg. The eggs of reptiles (including birds) and mammals have features that protect them from the challenges posed by a terrestrial (land) environment. In oviparous amniotes, the eggs are protected by a sturdy shell that safeguards the embryo against desiccation, although some air and moisture can pass through the shell. The amniote egg has several specialized compartments. The yolk sac holds the yolk that feeds the embryo. The allantois, which is an extension of the embryo's gut, stores solid waste products. Both the yolk sac and the allantois are connected to the developing embryo. Various other egg layers and membranes form around the ovum as it passes from the ovary through a muscular tube called the oviduct to the cloaca. The materials that make up these layers and membranes are secreted by specialized glands that line the oviduct. A clear fluid layer called the albumen—the "egg white" of a chicken egg—supplies the embryo with water and inorganic nutrients and cushions the embryo from impact if the egg is jarred or dropped. Albumen contains a protein (also called albumen), which binds to water and inorganic nutrients and aids in their transport. These nutrients diffuse through (pass through) the walls of the blood vessels that connect the embryo (through the umbilical cord) to the mother (at the placenta, or aggregation of vessels at the wall of the uterus/oviduct). The albumen is enveloped within the chorion, a thin membrane which also surrounds the embryo, yolk sac, and allantois. The chorion regulates the passage of gas and moisture into and out of the egg. Finally, a shell surrounds and protects the entire egg. The shell allows moisture and gas to pass through it. The shells of most lizards and snakes have a leathery consistency, whereas birds have hard, calcified shells that resist denting. see also Embryonic Development. Judy P. Sheen BibliographyCampbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. Biology, 5th ed. Menlo Park, CA: Addison Wesley Longman Inc., 1999. Jameson, E. W. Vertebrate Reproduction. New York: John Wiley & Sons, 1988. |
|
|
Cite this article
Sheen, Judy P.. "Egg." Animal Sciences. 2002. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. Sheen, Judy P.. "Egg." Animal Sciences. 2002. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1G2-3400500118.html Sheen, Judy P.. "Egg." Animal Sciences. 2002. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3400500118.html |
|
egg
egg it was traditionally thought that if a hen laid a very small egg it was unlucky; it was sometimes called a cock's egg, and believed capable of hatching a cockatrice or basilisk. Superstition also attached to the question of which end of a boiled egg should be opened; Sir Thomas Browne in Vulgar Errors (1650) notes that it was thought unlucky to crack an egg at the smaller end.
Egg Saturday and Egg Sunday former names for the Saturday and Sunday before Shrove Tuesday, traditionally a time of celebration before the rigours of Lent. scrambled egg informal term for gold braid on a military officer's cap. The expression is recorded from the mid 20th century. with egg on one's face appearing foolish or ridiculous. After the US presidential election of 2000, when the networks twice called the Florida election results prematurely and then had to retract, the journalist Tom Brokaw commented, ‘We don't just have egg on our face. We have omelette all over our suits.’ See also as good be an addled egg as an idle bird, chicken-and-egg, curate's egg, eggs, nest egg, roc's egg. |
|
|
Cite this article
ELIZABETH KNOWLES. "egg." The Oxford Dictionary of Phrase and Fable. 2006. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. ELIZABETH KNOWLES. "egg." The Oxford Dictionary of Phrase and Fable. 2006. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O214-egg.html ELIZABETH KNOWLES. "egg." The Oxford Dictionary of Phrase and Fable. 2006. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O214-egg.html |
|
egg
egg Hens' eggs are sold by size (EU); size 0 (weighs 75 g or more); size 1: 70 g; size 2: 65 g; size 3: 60 g; size 4: 55 g; size 5: 50–55 g (weighed with shell which is about 10% of the total weight). Useful in food preparation to thicken sauces and custard, as an emulsifier, to hold air in meringues and sponges, and as a binder in croquettes.
Average portion of two eggs is a rich source of vitamins D and B12; a good source of protein, niacin, and vitamins A and B2; a source of zinc; contains 170 mg of sodium; 13 g of fat, of which 35% is saturated and 50% mono‐unsaturated; supplies 175 kcal (735 kJ). The egg‐white is 60% of the whole and the yolk 30%. Duck eggs weigh about 85 g of which 10% is shell. One egg is a rich source of vitamins A, D, and B12; a good source of protein and vitamin B2; contains 90 mg of sodium and 9 g of fat of which 30% is saturated and 20% polyunsaturated; supplies 120 kcal (500 kJ). |
|
|
Cite this article
DAVID A. BENDER. "egg." A Dictionary of Food and Nutrition. 2005. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. DAVID A. BENDER. "egg." A Dictionary of Food and Nutrition. 2005. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O39-egg.html DAVID A. BENDER. "egg." A Dictionary of Food and Nutrition. 2005. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O39-egg.html |
|
egg
egg1 / eg/ • n. 1. an oval or round object laid by a female bird, reptile, fish, or invertebrate, usually containing a developing embryo. The eggs of birds are enclosed in a chalky shell, while those of reptiles are in a leathery membrane. ∎ an infertile egg, typically of the domestic hen, used for food. ∎ Biol. the female reproductive cell in animals and plants; an ovum. ∎ a thing resembling a bird's egg in shape: chocolate eggs. ∎ Archit. a decorative oval molding, used alternately with triangular figures. 2. inf., dated a person possessing a specified quality: she was a good egg. PHRASES: lay an egg inf. be completely unsuccessful; fail badly. with egg on one's face inf. appearing foolish or ridiculous. egg2 • v. [tr.] (egg someone on) urge or encourage someone to do something, esp. something foolish or risky. |
|
|
Cite this article
"egg." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "egg." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O999-egg.html "egg." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-egg.html |
|
egg
egg (ovum) Reproductive cell of female organism. Its nucleus supplies half the chromosome complement of a future zygote cell, and almost all the cytoplasm, upon union with the male gamete (sperm). Once fertilized, an animal egg is surrounded as it develops by albumin (egg white), shell, egg case, or membrane, depending on the species. The egg provides a reserve of food for the embryo in the form of yolk. Bird and insect eggs have a large yolk, mammalian eggs a much smaller one.
|
|
|
Cite this article
"egg." World Encyclopedia. 2005. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "egg." World Encyclopedia. 2005. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O142-egg.html "egg." World Encyclopedia. 2005. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-egg.html |
|
egg
egg In egg-laying animals (see ovipary and ovovivipary; compare vivipary), the fertilized ovum and the embryo into which it develops, enclosed within a protective egg membrane. The eggs of animals that are laid out of water have an impermeable outer covering (e.g. the shells of eggs laid by birds and reptiles) that protects them against drying.
|
|
|
Cite this article
MICHAEL ALLABY. "egg." A Dictionary of Ecology. 2004. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "egg." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O14-egg.html MICHAEL ALLABY. "egg." A Dictionary of Ecology. 2004. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-egg.html |
|
egg
egg
1. The fertilized ovum (zygote) in egg-laying animals, e.g. birds and insects, after it emerges from the body. The egg is covered by egg membranes that protect it from environmental damage, such as drying. 2. (or egg cell) The mature female reproductive cell in animals and plants. See oosphere; ovum. |
|
|
Cite this article
"egg." A Dictionary of Biology. 2004. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "egg." A Dictionary of Biology. 2004. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O6-egg.html "egg." A Dictionary of Biology. 2004. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O6-egg.html |
|
egg
egg1 ‘ovum’. XIV. — ON.; superseding cognate ME. ey :- OE. ǣġ = OS., (O)HG., Du. ei :- Gmc. *ajjaz- n., rel. to L. ōvum, Gr. ōión, Ir. og, W. wy, and poss. further to words for ‘bird’ in Skr. ví-, L. avis.
|
|
|
Cite this article
T. F. HOAD. "egg." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "egg." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O27-egg.html T. F. HOAD. "egg." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-egg.html |
|
egg
|
|
|
Cite this article
T. F. HOAD. "egg." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "egg." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O27-egg1.html T. F. HOAD. "egg." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-egg1.html |
|
egg
egg see ovum . |
|
|
Cite this article
"egg." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "egg." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1E1-X-egg.html "egg." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-X-egg.html |
|
egg
egg
•beg, cleg, egg, Eigg, Greg, keg, leg, Meg, peg, skeg, teg, yegg
•filibeg • blackleg • peg-leg • dogleg
•foreleg • Oleg • bootleg • nutmeg
•Winnipeg • clothes peg • thalweg
|
|
|
Cite this article
"egg." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "egg." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O233-egg.html "egg." Oxford Dictionary of Rhymes. 2007. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O233-egg.html |
|
Search over 100 encyclopedias and dictionaries:
HighBeam™ Research, Inc. © Copyright 2012. All rights reserved.
The Encyclopedia.com advertising network includes:
