Why does the fragmentation of a fertilized egg in chicken and rabbit happen differently?

In the rabbit egg, the crushing is complete. When completely crushed, the plane of the first division corresponds to the plane of bilateral symmetry. The plane of the second division extends perpendicular to the plane of the first. Both furrows of the first two divisions are meridian, i.e. start at the animal pole and extend to the vegetative pole.
Partial fragmentation in the chicken ovum covers only the yolk-free cytoplasm. It is located in the form of a thin disk at the animal pole, therefore this type of crushing is called discoidal.
This is explained by various ways of embryo ontogenesis and the need for the accumulation of nutrients in the egg.

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