Neither first nor last of little eggs developing naturally (2,5)
I believe the answer is:
in utero
'developing naturally' is the definition.
'in utero' can be an answer for 'developing' (I've seen this in another clue). I'm not certain of the 'naturally' bit.
'neither first nor last of little eggs' is the wordplay.
I cannot quite see how this works, but
'first' could be 'i' (I in Roman numerals eg Elizabeth I) and 'i' is located in the answer.
'last' could be 't' (I've seen this in other clues) and 't' is present in the answer.
'of' could be 'o' and 'o' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for in utero that I've seen before include "Before birth (Latin)" , "Embryonic" , "Where the foetus is" , "Before birth - routine (anag)" , "Pre-natal position (Latin)" .)