In the following pages data will be given about the size of the megalospheric embryonic apparatus, and of the size of the shell, of some Foraminifera. By comparing these data for a certain species from different samples, the relative ages of which are known, it will be possible, to get an insight into the alterations of the measured characters in geological times. For that purpose samples from geological sections, or otherwise well defined geological formations, were used. A description of each of these sections will be given, in order to discuss the reliability of the determinations of the relative ages of the samples. I may point out here, that as the layers containing the foraminiferal shells have a certain thickness, and as the sampling has been done over the whole width of the outcropping layer, or over part of it, we may be certain, that the deposition of these shells, must have taken “many years”. In my opinion this may be an advantage, as the possible annual or short-periode influence of the environment on the phaenotype may thus have been eliminated.