When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male.
The larva has grown around the remains of the yolk and the remains of the soft, transparent egg are discarded. Young little developed with indistinct larval stage in monotremes and marsupials, direct development in placentals.ĭiagram of a fish egg: A. Macrolecithal eggs in monotremes and marsupials, extreme microlecithal eggs in placental mammals. The young more or less fully developed, no distinct larval stage. Large to very large macrolecithal eggs in all species, develop independent of water. Large macrolecithal eggs, develop independent of water. Tadpole stage, direct development in some species. Medium-sized mesolecithal eggs in all species. Larval stage, ovovivipary in some species. Macrolecithal eggs, small to medium size, large eggs in the coelacanth ĭirect development, viviparity in some species Larval stage in lampreys, direct development in hagfish. Mesolecithal eggs, especially large in hagfish Several major groups of animals typically have readily distinguishable eggs. Reproductive structures similar to the egg in other kingdoms are termed " spores", or in spermatophytes " seeds", or in gametophytes "egg cells".
: 132 Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller. The bee hummingbird produces the smallest known bird egg, which measures between 6.35–11.4 millimetres (0.250–0.449 in) long and weighs half of a gram (around 0.02 oz). At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird, : 130 though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. Whale shark eggs typically hatch within the mother. The largest recorded egg is from a whale shark and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Most arthropods, vertebrates (excluding live-bearing mammals), and mollusks lay eggs, although some, such as scorpions, do not. Six commercial eggs - view from the top against a white backgroundĪn egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the animal hatches. Membranes: allantois, chorion, amnion, and vitellus/ yolk. (Click on image for key) Diagram of a chicken egg in its 9th day. JSTOR ( February 2019) ( Learn how and when to remove this template message)Įggs of various birds, a reptile, various cartilaginous fish, a cuttlefish and various butterflies and moths.Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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