Petri dishes containing unfertilised human ova (eggs), prepared prior to being mixed with human sperm at the ^Iin vitro^i fertilisation unit at the Cromwell Hospital, London. The ova are removed from the potential mother and pipetted into the dishes (2-3 in each dish). The pink colour of the medium in which they are suspended is due to an acid-base indicator (pH & temperature are critical factors). Cleanliness is also vital