Search through what grows on layer (4)
I believe the answer is:
comb
I believe this is a double definition.
'search' is the first definition.
(combing is a kind of searching)
'what grows on layer' is the second definition.
(crest on a chicken, something which lays eggs)
'through' acts as a link.
(Other definitions for comb that I've seen before include "Used to tidy hair" , "Honey structure" , "Tidy (hair); some honey" , "Untangle (hair)" , "Common hair tidier" .)