During sexual reproduction of Pseudourostyla there are four rounds of cortical reorganization in all. The first one is initiated in anaphase of the first meiotic division and com- pleted after separation of the conjugating mates into two exconjugants.The exconjugants have not UM

and about half of them do not possess buccal cirrus.The cytopharynx remains vestigial. The number of new AZM membranelles and other cirri is reduced compared to the vegetative cell.Afterwards

all or almost all ciliatures generated during the first reorganization disappear with the forma tion of the spherical paracyst.The second round begins towards the end of the paracyst stage

when the macronuclear anlage from which a vacuolated mass of DNA-poor ma- terial has been extruded

contracts.The second cortical development completes shortly before the macronuclear anlage divides or after it has generated 3-9macronuclei

and a micronucleus en- ters the first mitotic telophase

The cell gains a new UM

and a normal cytopharynx

and about two thirds of cells have buccal cirrus.The number of new AZM membranelles and other cirri is more reduced in contrast to the cell after the first reorganization. The third round follows closely the second.During the period

the development of ciliary primordia exhibits the same temporal sequence and spatial pattern as in physiological reorganization

but behavior of all 3-9 macronuclei which merge into a single whole first and then divide repeatedly is similar to that in binary fission

After the third reorganization

the cell possesses normal ciliature

but the number of membranelles and cirri remains reduced.Finally

the fourth round comes when the cell has about 20(13 ～ 30 ) macronuclei.The process and the way in the fourth is the same as in the third.After the fourth reorganization

the cell recovers the normal ciliature of the vegetative cell and undergoes the first binary after conjugation in one day.