An egg is a zygote-containing organic vessel in which the animal embryo develops until it can survive by itself; at that moment the animal hatched. Eggs result from egg fertilization. Most arthropods, vertebrates, and mollusks lay eggs, though some, such as scorpions and most mammals, do not.
Reptile eggs, bird eggs, and monotestic eggs are placed on water, and are surrounded by a protective shell, either flexible or inflexible. Eggs that are placed on the ground or in the nest are usually stored in warm and favorable temperatures while the embryo grows. When the embryo develops enough to hatch, ie breaks from the eggshell. Some embryos have temporary egg teeth that they use to crack, squeeze, or break the eggshell or cover.
The largest recorded egg comes from whale sharks, and measures 30 cm - 11.5 cm - 11.5 cm (11.8 inches - 5.5 in 3.5 inches). Egg whale eggs usually hatch inside its mother. Weighing 1.5 kg (3.3 pounds) and up to 17.8 centimeters (Â ± 5.5 cm), the ostrich egg is the largest egg of every living bird, though elephant birds are extinct and some dinosaurs have eggs the greater one. Hummingbird bees produce the smallest known bird egg, which weighs half a gram (about 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects and other invertebrates can become smaller.
Reproductive structures similar to eggs in other kingdoms are called "spores," or in "seeds" spermatophytes, or in "egg cell" gametophytes.
Video Egg
Eggs of different animal groups
Some large groups of animals usually have eggs that are easily distinguished.
Fish and amphibian egg
The most common reproductive strategy for fish is known as oviparity, in which females lay undeveloped eggs that are fertilized externally by males. Usually large quantities of eggs are placed at one time (adult female cods can produce 4-6 million eggs in one spawning) and the eggs are then allowed to flourish without primary care. When larvae hatch from eggs, they often carry the remnants of egg yolks in yolk sacs that continue to fertilize the larvae for several days as they learn to swim. Once the yolk is consumed, there is a critical point after that they must learn how to hunt and feed or they will die.
Some fish, especially rays and most sharks use ovoviviparity in which the egg is fertilized and develops internally. But the larvae still grow in eggs that eat egg yolks and no food directly from their mother. The mother then gave birth to a relatively adult young man. In certain cases, the most physically advanced offspring will devour their smaller siblings for further nutrition while still inside the mother's body. This is known as intrauterine cannibalism.
In certain scenarios, some fish such as hammerhead sharks and reef sharks are vivipar, with eggs fertilized and developed internally, but with mom also providing direct food.
The fish and amphibian eggs were like jam. Cartilagenous fish (shark, roller skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide range of internal and external embryonic developments. Most fish species spawn externally fertilized eggs, usually with male insemination in egg cells after the female spawns. These eggs do not have a shell and will dry out in the air. Even air-breathing amphibians lay eggs in water, or in protective foams as well as foam-noc Coast exhaust trees, Chiromantis xerampelina .
Bird Egg
Bird eggs are laid by females and incubated for a time varying according to species; one young hatch of each egg. The average clutch size ranges from one (as in condors) to about 17 (gray partridge). Some birds lay eggs even when not fertilized (eg hens); it is not uncommon for pet owners to find their single bird nesting over an unfertilized egg clutch, sometimes called a wind egg.
Color
The default color of vertebrate eggs is white from calcium carbonate from which the shell is made, but some birds, especially passerines, produce colored eggs. The biliverdin and zinc chelate pigments provide a green or blue color, and protoporfirin produces red and brown as the base color or spotting.
Non-passerines usually have white eggs, except in some groups that nest on the ground like Charadriiformes, sandgrouse and nightjars, where camouflage is needed, and some parasitic cuckoos that must match the peduncle's host egg. Most passerines, by contrast, lay their eggs in color, even if they do not need vague colors.
But some people argue that the protoporphyrin sign on passerine eggs actually acts to reduce the fragility by acting as a solid state lubricant. If not enough calcium is available in local soil, the eggshell may be thin, especially in the circle around the broad end. Spekulus protoporfirin compensates for this, and increases inversely with the amount of calcium in the soil.
For the same reason, then the egg in the clutch is more visible than the beginning because the female calcium supply is depleted.
The egg color of individuals is also genetically influenced, and appears to be inherited through the mother alone, indicating that the gene responsible for pigmentation is in the sex that determines the W chromosome (female bird is WZ, male ZZ).
It used to be thought that color was applied to the shell immediately before laying eggs, but this study showed that staining is an integral part of the development of the shell, with the same protein responsible for storing calcium carbonate, or protoporfirin when there is a lack of it.
In species such as the common guillemot, which is nested in large groups, each female's egg has a very different mark, making it easier for females to identify their own eggs on the cliff edge of the cliff where they breed.
Shell
Eggshell birds are varied. As an example:
- crude and calcareous cormorant egg
- shiny tinamou egg
- oily and waterproof duck egg
- Cassowary eggs are pitted against
The small pores in the egg shell allow the embryo to breathe. Domestic chicken eggs have about 7000 pores.
Shape
Most bird eggs have an oval shape, with one rounded tip and the other end more pointed. This form results from eggs being forced through the fallopian tubes. Muscles hold the egg tube behind the egg, pushing it forward. The egg wall can still be formed, and the pointed tip develops in the back. Long, pointy eggs are an incidental consequence because they have a distinctively slender body of birds with a strong flying ability; the flight narrows the fallopian tubes, which alter the type of egg the bird can lie on. Crowded birds often have very conical eggs. They tend to roll over, tend to turn around in tight circles; this nature tends to arise because of evolution through natural selection. In contrast, many bird-laying holes have almost spherical eggs.
Predation
Many animals eat eggs. For example, the primary predators of black oystercatcher eggs include raccoon, skunk, mink, river and sea otter, gulls, crows and foxes. Stoat ( Mustela erminea ) and long tailed foxes ( M. Frenata ) stole duck eggs. Snakes from the genus Dasypeltis and Elachistodon specialize in eating eggs.
Brood parasitism occurs in birds when one species puts its egg in another. In some cases, the host egg is removed or eaten by the woman, or expelled by her girl. Parent parasites include cowbirds and many cuckoo Old World.
Various instances
Amniote eggs and embryos
Like amphibians, amniotes are air-breathing vertebrates, but they have elaborate eggs or embryos, including amniotic membranes. Amniotas include reptiles (including dinosaurs and their descendants, birds) and mammals.
Reptile eggs are often rubbery and always white. They are able to survive in the air. Often the gender of the developing embryo is determined by the temperature around it, with a cooler temperature that benefits men. Not all reptiles lay their eggs; there is a vivipar ("live birth").
Dinosaurs lay eggs, some of which have been preserved as petrified fossils.
Among mammals, early extinct species lay eggs, as do platypus and ekidna (antlers of thorns). The platypus and two genera echidna are Australian monotremes. Mammalian and placental mammals do not lay eggs, but their young unborn have complex networks that identify amniotes.
Mammalian egg
Egg-laying eggs (platypus and echidnas) are macrolecithal eggs very similar to reptiles. Marsupial eggs are also macrolecithal, but rather small, and develop in the female body, but do not form the placenta. The young are born at a very early stage, and can be classified as "larva" in a biological sense.
In placental mammals, the egg itself is empty of egg yolks, but it develops the umbilical cord from a structure that in reptiles will form a yolk sac. Receiving nutrition from the mother, the fetus completes the development while in the womb.
Invertebrate eggs
Common eggs among invertebrates, including insects, spiders, mollusks, and crustaceans.
Maps Egg
Evolution and structure
All sexual reproductive lives, including plants and animals, produce gametes. Male gamete cells, sperm, are usually motile while female gamete cells, ovum, are generally larger and sessile. Male and female gametes combine to produce zygote cells. In multicellular organisms, the zygote then divides organized into smaller, more specialized cells, so that the new individual develops into an embryo. In most embryo animals is the initial stage of sessile of the individual life cycle, and is followed by the appearance (ie, hatching) of the motile stage. The zygote or the ovum itself or an organic sessile container containing the developing embryo may be called an egg.
Recent proposals suggest that phylotypic animal body plans originate from cell aggregates prior to the developmental stage of eggs. Eggs, in this view, are then an evolutionary innovation, selected for their role in ensuring genetic uniformity among the cells of newly formed multicellular organisms.
Scientific classification
Scientists often classify animal reproduction according to the level of development that occurs before new individuals are excluded from the adult body, and by egg yolks provided eggs to fertilize the embryo.
Egg and egg yolk
Vertebrate eggs can be classified by the relative amount of egg yolks. A simple egg with a small yolk is called microlecithal, medium-sized eggs with some egg yolks called mesolecithal , and large eggs with large yellow concentrates are called macrolecithal Microlecithal
Small eggs with little yellow are called microlecithal. The yolk is distributed evenly, so the egg division cuts and divides the egg into cells of similar size. In sponges and cnidarians, dividing eggs develop directly into simple larvae, such as morula with cilia. In cnidaria, this stage is called a planula, and develops either directly into adult animals or forming new adult individuals through the process of budding.
Microlecithal eggs require minimal yellow masses. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, lancelets and most marine arthropods. In animals that are anatomically simple, such as cnidarians and flatworms, fetal development can be very short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large quantities. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter is more complex anatomically than mis. flatworms, and small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be very different from that of an adult animal.
In placental mammals, in which the embryo is nurtured by the mother during the entire fetal period, the egg is reduced in size to a bare egg.
Mesolecithal
Mesolecithal eggs have more yolks than microlecithal eggs. The yolk is concentrated in one part of the egg ( vegetal pole ), with the cell nucleus and most of the cytoplasm on the other side (the animal pole ). Cell division is uneven, and is mainly concentrated in the polar animals that are rich in cytoplasm.
The greater yolk content of mesolecithal eggs allows for longer fetal development. Animals that are anatomically simplistic will be able to go through full development and leave eggs in a form that is reminiscent of adult animals. This is a situation found in hagfish and some snails. Animals with smaller egg sizes or more advanced anatomy will still have different larval stages, although the larvae are essentially the same as the mature animals, as in lampreys, coelacanths and salamanders.
Macrolecithal
Eggs with large yellow are called macrolecithal. Eggs are usually few in number, and the embryo has enough food to undergo fetal development fully in most groups. Macular eggs are found only in selected representatives of two groups: Cephalopods and vertebrates.
Egg macrolis through various types of development compared to other eggs. Due to the large size of the yolk, cell division can not break the mass of the yolk. The fetus develops as a plate-like structure over the mass of the yolk, and just wraps it in the next stage. Some of the yolk mass still exists as an external or semi-external yolk sac on hatching in many groups. This form of fetal development is common in bony fish, although their eggs can be very small. Despite their macrolecithal structure, small size eggs do not allow for direct development, and the eggs hatch to the larval stage ("fry"). In terrestrial animals with macrolecithal eggs, large volumes for surface ratios require structures to aid the transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or poison from its own feces while in the egg, see amniote.
In addition to bony fish and cephalopoda, macrolecithal eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals. Coelacanth eggs can reach a size of 9 cm in diameter, and the young undergo a full development while in the uterus, living in excessive yolk.
Egg reproduction
Animals are usually classified according to their mode of reproduction, at the most general level that distinguishes laying (Latin from oviparous) from the live-carrier (Latin viviparous ).
This classification is divided into more detail in accordance with developments that occur before the offspring are removed from the adult body. Traditionally:
- Ovuliparity means women grow unfertilized eggs (ovum), which must then be fertilized externally. Ovuliparitas is typical of bony fish, anura, echinodermata, bivalvia and cnidaria. Most of the aquatic organisms are ovuliparous. This term comes from the diminiutive meaning of "small egg".
- Oviparity is where fertilization occurs internally so that the eggs placed by women are zygotes (or new embryos), often with important external tissues added (eg, in chicken eggs, no part outside the egg yolk comes with a zygote). A typical oviparity of birds, reptiles, some cartilaginous fish and most arthropods. Terrestrial organisms are usually ovipar, with egg sheaths that retain moisture vaporization.
- Ovo-viviparity is where the zygote is stored in the adult body but there is no interaction trofik (feeding). That is, the embryo still gets all the nutrients from the egg. Most fish, amphibians, or reptiles that live in the womb are actually ovoviviparous. Examples include the reptile Anguis fragilis , the seahorse (where the zygote is stored in the abdomen of a male "marsupium"), and the Rhinoderma darwinii frog (where the egg develops in the vocal sac) and Rheobatrachus (where the egg cell develops in the abdomen).
- histotropic viviparity means the embryo develops in the female oviduct but obtains nutrients by consuming another egg, zygote or embryo (oophagy or adelphophagy). This intra-uterine cannibalism occurs in some sharks and in the black salamanders Salamandra atra . Marsupials excrete "uterine milk" which complements food from egg yolk sack.
- hemotropic viviparity is where the nutrients are administered from a woman's blood through a prescribed organ. This most commonly occurs via the placenta, found in most mammals. A similar structure is found in some sharks and in the pseudomoia pagenstecheri lizard. In some hylid frogs, the embryo is fed by the mother through a special gill.
The term hemotropic originates from Latin for blood giving, in contrast to histotropic for tissue feeding.
Human use
Food
Eggs laid by many species, including birds, reptiles, amphibians, and fish, may have been eaten by humans for thousands of years. Popular choices for egg consumption are chicken, duck, egg, and caviar, but with wide margins, the eggs most often consumed by humans are chicken eggs, usually not fertilized.
Egg and Kashrut
According to Kashrut, that's the set of Jewish dietary laws, halal food can be consumed according to halakha (Jewish law). Halal meat (or derivatives) can not be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (both meat and milk) although it is an animal product and can be mixed with milk or halal meat. Mayones, for example, are usually marked "pareve" even though the definition contains eggs.
Vaccine Making
Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that rickettsia and viruses that cause various diseases will grow in chicken embryos. This allows the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky spotted fever and other diseases.
Culture
Eggs are a symbol of new life and rebirth in many cultures around the world. Christians view Easter eggs as a symbol of the resurrection of Jesus Christ. The popular Easter tradition in some parts of the world is a boiled egg ornament (usually by dipping, but often with spray painting). Adults often hide eggs for children to discover, an activity known as Easter egg hunts. A similar tradition of egg painting exists in regions of the world that are influenced by Persian culture. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and puts it together in a bowl. The tradition of dancing eggs was held during the feast of Corpus Christi in Barcelona and other Catalan cities since the 16th century. It consists of an empty egg, positioned on top of a water jet from a fountain, which starts spinning without falling.
Although food, eggs are sometimes thrown at home, cars, or people. This act, known generally as "egging" in many English-speaking countries, is a small form of vandalism and, therefore, is usually a criminal offense and capable of damaging property (egg whites can degrade certain types of paint) as well. as a cause of serious eye injury. On Halloween, for example, a trick or processor has been known to throw an egg (and sometimes flour) on the property or people who do not receive anything. Eggs are also often thrown into protests, as they are cheap and not lethal, but are very messy when broken.
Collecting
Egg collection is a popular hobby in many contexts, including among the first Australians to love this practice. Traditionally, the embryo will be discarded before the collector keeps the eggshell.
Collecting wild bird eggs is now banned by many countries and regions by considering threats to endangered species. In the United Kingdom, the practice was banned by the 1954 Wildlife and Wildlife Act and Village 1981. On the other hand, ongoing underground trade became a serious problem.
Since the protection of wild bird eggs has been arranged, the initial collection has come to the museum as a curiosity. For example, the Australian Museum hosts a collection of about 20,000 registered egg shells, and collections at the Western Australian Museum have been archived in a gallery. Scientists regard the collection of eggs as a good natural history data, since the details recorded in the collector's records have helped them understand the nesting behavior of birds.
Gallery
See also
References
Source of the article : Wikipedia
0 Comments