Stomatogenesis during sexual and asexual reproduction in an amicronucleate strain of Paramecium caudatum.

Amicronucleate cells of Paramecium caudatum, whose micronuclei have been artifically removed by micropipetting, are characterized by the appearance of a deciliated area at the posterior part of the buccal opening. These cells form food vacuoles at a slightly lower rate than micronucleate cells. Their mean interfission time is longer than that in micronucleates. The exconjugants of amicronucleate cells can not form food vacuoles and eventually die witout fission, though conjugation proceeds normally in them as well as in their micronucleate mate. The oral apparatus of amicronucleate exconjugants seems to be shallower than that of micronucleates. The membranellar cilia, therefore, can be seen through the buccal overture by scanning electron microscope. The results obtained from the cross of micronucleate and amicronucleate strains and from the induction of autogamy in amicronucleate strains suggest that the micronucleus has a primary role in developing the normal oral apparatus after nuclear reorganization.