Classification of eggs which is based on the amount of yolk, based on the distribution of yolk and other types of eggs.
- On the Basis of the Amount of yolk types of eggs are
- Alecithal Egg: When the egg contains no yolk, it is called alecithal egg.
- Microlecithal Egg: When the egg contain small or negligible amount of yolk it is said to be microlecithal.
- Mesolecithal egg: The amount of yolk present is moderate and is not high.
- Macrolecithal/Megalecithal Egg: When the egg contains large amount of yolk it is said to be macrolecithal or megalecithal egg.
- On the Basis of the distribution of yolk types of eggs are
- Isolecithal/Homolecithal Egg: ln isolecithal eggs, the very little amount of yolk present is uniformly distributed throughout the ooplasm.
- Telolecithal Egg: In eggs containing moderate or large quantity of yolk, the distribution of yolk is not uniform. lt is concentrated more towards the vegetal pole.
- Telolecithal eggs may further classified into three types:
1.Slightly Telolecithal
2.Moderately Telolecithal
3.Extremely Telolecithal
- Telolecithal eggs may further classified into three types:
- Centrolecithal Egg: They are relatively large and elongate and have a very great amount of yolk. The nucleus lies at the geometric centre of the yolk mass, surrounded by a small amount of cytoplasm. A thin cytoplasmic layer covers the surface of the yolk.
- Other types are
- Mosaic egg: ln certain eggs, every portion is predetermined with respect to its potentialities for further development.
- Regulative egg: ln vertebrates and most of the invertebrates, the developmental potentialities are not predetermined in the eggs.
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