Naturalist in ward for treatment (6)
I believe the answer is:
darwin
'naturalist' is the definition.
(Darwin is an example)
'in ward for treatment' is the wordplay.
'for treatment' is an anagram indicator (I've seen this in other clues).
'in'+'ward'='inward'
'inward' with letters rearranged gives 'DARWIN'.
(Other definitions for darwin that I've seen before include "Australian port, capital of the Northern Territory" , "Find the naturalist askey in ward 96)" , "Originator of the theory of evolution" , "Naturalist with a theory on evolution" , "Man of note" .)