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The egg cell is generally asymmetric, having an animal pole (future ectoderm). It is covered with protective envelopes, with different layers. The first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane (zona pellucida in mammals).
The only living mammals that lay eggs are echidnas and platypuses. In the latter, the eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally). [11] After laying her eggs, the female curls around them.
Males fertilize the eggs, then defend and clean the nest while embryos develop. Toadfish embryos are large and, as a result, have been studied for over a century. [4] After about 4 weeks the eggs hatch. At first, the young toadfish stay attached to the yolk. When the yolk has been absorbed for energy, the young toadfish learn to swim.
The eggs have an average diameter of 1 millimetre (0.039 in). The eggs are generally surrounded by the extraembryonic membranes but do not develop a shell, hard or soft, around these membranes. Some fish have thick, leathery coats, especially if they must withstand physical force or desiccation. These type of eggs can also be very small and ...
When mating, the female seahorse deposits up to 1,500 (average of 100 to 1,000) eggs in the male's pouch, located on the ventral abdomen at the base of the tail. Male juveniles develop pouches when they are 5–7 months old. The male carries the eggs for 9 to 45 days until the seahorses emerge fully developed, but very small.
Per the FDA, for the best quality, you should use eggs within three weeks of their purchase date. Donovan, however, gives a slightly longer shelf life—six weeks in the fridge for farm-fresh eggs ...
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Most bony fish eggs are referred to as telolecithal which means that most of the egg cell cytoplasm is yolk. [1] The yolky end of the egg (the vegetal pole) remains homogenous while the other end (the animal pole) undergoes cell division. [2]