The spindle in determinate cleavage is

The correct option is Oblique.

To understand why the mitotic spindle is oriented obliquely during determinate cleavage, we must look at the characteristics of this developmental pattern.

Determinate cleavage (also known as mosaic cleavage) is a form of embryonic development found in many protostomes (such as molluscs and annelids). In this type of cleavage, the developmental fate of each individual cell (blastomere) is established very early in development. If a cell is isolated or removed at an early stage, the resulting embryo will be incomplete, lacking the structures that the removed cell was destined to form.

This early determination of cell fate is structurally driven by the precise orientation of the mitotic spindle during cell divisions. Rather than dividing strictly along horizontal (equatorial) or vertical (meridional) axes, the spindle forms at an oblique angle relative to the polar axis of the egg cell. This oblique orientation leads to spiral cleavage, where the upper tier of blastomeres is rotated relative to the lower tier, ensuring unequal distribution of cytoplasmic determinants and establishing the mosaic developmental pathways of the daughter cells.