Removal includes cells (3)
I believe the answer is:
'cells' is the definition.
(ovum is a kind of cell)
'removal includes' is the wordplay.
'includes' indicates the answer is hidden within the clue.
'OVA' is hidden in the letters of 'removal'.
(Other definitions for ova that I've seen before include "Release of women" , "Prerequisite for procreation" , "Female egg-cells" , "Multiple Latin eggs" , "Potential life sources" .)