It is different from EP in that meiosis has occurred and the haploid set of chromosomes of the female have replicated themselves prior to the 1st cell division. They are, therefore, homozygous for every gene. Heat shock prevents the first cell division by some unknown mechanism, thus restoring diploidy in some embryos. Eggs are squeezed from the female and fertilized with UV-irradiated sperm. It is very difficult to stop the first mitotic division.
Homozygous diploids can be fertile males or females.
The thin plastic of the cylinders transfers very little heat or cold. The temperature of the 41C bath is held very accurately. Too low a temperature produces haploids and too high a temperature kills embryos. Different strains may require a slightly different temperature. An immersible stirrer drives a magnetic stirring bar in the 41C beaker to keep the temperature uniform.