Classification based on amount of yolk:

1. Alecithal:

Here there is no yolk in the egg. Eg., eutherian mammals.

2. Microlecithal:

ADVERTISEMENTS:

Eggs have a small amount of yolks, eg., amphioxus.

3. Mesolecithal:

Eggs have a moderate amount of reserve food material eg., amphibians like salamander, frog, toads etc.

4. Macrolecithal or polylecithal:

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These eggs have a large amount of yolk and also a little quantity of yolk free cytoplasm. Eg. Reptiles, birds and prototherian mammals.