| Abstract: | ABSTRACT Amicronucleate Paramecium tetraurelia fails to develop an oral apparatus but resorbs the pre-existing one in the sexual cycle. Previous cytological studies have revealed the presence of a shallow, oral depression with a few scattered basal bodies after autogamy or conjugation. The present ultrastructural study of the ectoplasm beneath the oral depression revealed only the presence of a disorganized filamentous reticulum and small blocks of cytopharyngeal ribbons. In addition, beneath the oral depression, a large number of discoidal vesicles were found, similar to but larger in diameter than those normally associated with the cytopharynx of vegetative cells. The oral structures found in amicronucleates in autogamy might be remnants of the pre-existing oral apparatus, but the possibility that they were newly developed was not excluded. The morphogenetic interest of these structures was discussed. It is evident that amicronucleates in autogamy do not develop an extensive oral ultrastructural organization. |
