But this business of mating types is a very peculiar business. During the day, one clone will be of mating type 1 and will mate only with mating type 2. At dusk, members of the clone will not mate at all. By nightfall, the mating type 1s will have changed into 2s and will thus refuse to mate with other mating type 2s. By changing the lighting conditions, making 'dawn' and 'dusk' come at different times, the formation of different sexes or mating types in these paramecia can then be controlled.
Mating type is determined by the presence of proteins on the surface of the cilia.
Now, if there is no other mating type available, then Lacrymaria may simply start dividing up its own genetic material into six, eight, or more pieces and begin a process of repair and recombination. The mechanism is called autogamy . After this reorganization, the organism can then begin to reproduce again by division. Certain conditions obtain for autogamy to take place and the cells must still be healthy enough to undergo this radical repair process. If the conditions are not right, then the organism will reach a limit in terms of the number of times it can divide, and the culture will die out.