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". 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 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, 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. An egg results from fertilization of an egg cell. Six commercial eggs - view from the top against a white backgroundĪn egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal hatches.
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