PLANE OF CLEAVAGE -

• Each cleavage of the division zygote is marked by a cleavage furrow.
• Usually the first cleavage furrow is vertical & passes through the main axis of the egg.
• The second cleavage furrow is also vertical but at right angle to the first one.
• The third cleavage furrow is horizontal or parallel to the equator.
• These planes are of 4 types -

1. Meridional plane - Cleavage forrow passing through the middle, animal vegital poles axis. eg. Amphioxis, frog and first cleavage of chick.

2. Vertical or longitudinal plane - The vertical cleavage pass through the animal & vegital pole but not through the median axis. The cleavage furrow pass either to the right or left of the axis. eg. III cleavage of chick.

3. Equitorial plane - The cleavage furrow is horizontal / transverse and it pass between the animal & vegital pole. eg. I cleavage of the higher mammals including man.

4. Lattitudinal plane - The previous furrow is transversely or horizontally not on the equator. eg. III cleavage in the egg of amphioxis and frog.