Classification based on amount of yolk:
1. Alecithal:
Here there is no yolk in the egg. Eg., eutherian mammals.
2. Microlecithal:
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:
These eggs have a large amount of yolk and also a little quantity of yolk free cytoplasm. Eg. Reptiles, birds and prototherian mammals.