Layer seen in ozone hole reversed (3)
I believe the answer is:
hen
'layer' is the definition.
(something which lays - eggs in this case)
'in ozone hole reversed' is the wordplay.
'in' says the answer is hidden in the clue.
'reversed' says the letters should be written in reverse.
'neh' is hidden in the letters of 'ozone hole'.
'neh' in reverse letter order is 'HEN'.
'seen' is the link.
(Other definitions for hen that I've seen before include "Not cock" , "Source of eggs" , "Composed of women" , "Laying bird" , "Female bird" .)