Periderm week 17

Regression begins at week 17-18. The periderm cells flatten and the blebs diminish significantly in height. The glycogen content of the cells decreases until it is gone by week 20.

Regression begins

Note the periderm cells now and compare their appearance to week 16. The periderm cells are now flattened and overlie the keratinocytes which are defined by their desmisomal junctions.