telolecithal yolk

embryology

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July 14, 2026

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In embryology, telolecithal yolk refers to eggs with abundant yolk concentrated in one hemisphere. This type of yolk distribution is found in many invertebrates and vertebrates below marsupial mammals. In contrast, eggs with little, uniformly distributed yolk are called isolecithal, occurring in invertebrates and most mammals.1

Eggs are classified by their yolk content. Oligolecithal eggs have a small amount of evenly distributed yolk. Telolecithal eggs have unevenly distributed yolk, concentrated towards the vegetal pole. Megalecithal eggs contain very large amounts of yolk. The yolk serves as nourishment for the developing embryo. The pattern of early cell division, known as cleavage, can be influenced by the amount and distribution of yolk.213

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yolk
…of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than marsupial mammals. In arthropods, the yolk is massed near the centre of the egg; such eggs are termed centrolecithal.
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…of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than marsupial mammals. In arthropods, the yolk is massed near the centre of the egg; such eggs are termed centrolecithal.
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animal development
Preparatory events
…towards the vegetal pole) is telolecithal; and one with still greater amounts of yolk in granules or in a compact mass is megalecithal.
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…towards the vegetal pole) is telolecithal; and one with still greater amounts of yolk in granules or in a compact mass is megalecithal.
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