The fertility test undertaken on partially incubated eggs requires the destruction of some hatching eggs,but is easier and requires considerably less practice then examining fertility in un incubated eggs ,once again a 100 eggs sample per flock is the minimum requirement ,although it is usually more practical to use one or more full setter try.Eggs should have been incubated for 3 to 5 days proir to examination each egg should be opened very carefully from the top of the air cell so as to avoid any disruption to the egg contants,then the blastoderm or infertile disc will be on th upper surface of the yolk and very easy to see.do not spend too much time trying to identify signs of membrane development if it is not obvious it has not happened