During the binary division of Pseudourostyla cristata

the new adoral zone of membranelles(AZM) in the proter is generated from three parts

namely the membranelles assembled by the AZM primordium which connects with the posterior end of the old AZM to form a complcx

the old AZM lapel modified by cutting out about 25 membranelles from the anterior section and the old AZM collar whose several membranelles in both sides have disintegrated. The AZM membranelle number in the proter is regulated and controlled to an appropriate range by addition of new membranelles and reduction of some old ones. The same developmental programming of “addition and subtraction” is also applied to the morphogenesis of cells during physiological reorganization and cells in the 3rd and 4th cortical reorganizations during conjugation in P. cristata. This suggests that there would be simplification of genetical system of P. cristata in evolution

which is convenient for the genetic control.