Conjugation in Kahlia sp. with Special Reference to Meiosis and Endomitosis

SYNOPSIS. During conjugation of Kahlia the micronuclei divide 3 times before synkaryon formation and 2 times thereafter. The 1st division is heterotypic, as in other ciliates, in that it is characterized by the parachute stage. Following this stage, 24 to 26 bivalents and 4 to 8 univalents appear in the micronuclear area. When the bivalents move to organize the metaphase plate, the univalents lag behind and fail to reach the equatorial region at the same time. Due to this irregular behavior of the univalents there is no distinct metaphase in the first meiotic division. A few meiotic irregularities including the breakdown of the spindle apparatus have been observed. During the breakdown of the spindle apparatus the chromosomes fuse into irregular bodies which resemble the chromosome aggregates observed during the somatic divisions. Generally 1, and rarely more, of the products of the 1st division enter the 2nd division. The spindles of this division are oriented parallel to the long axis of the cell, and 1 of the daughter nuclei reaches the partition membrane separating the conjugants. This nucleus alone undergoes the 3rd division, resulting in the formation of gametic nuclei. Reciprocal exchange and fusion of the gametic nuclei result in the synkaryon formation. The synkaryon divides twice in rapid succession resulting in 4 daughter nuclei; 1 of them degenerates and 2 condense and become functional micronuclei. The chromosomes of the remaining daughter nucleus resemble in size and number the bivalents of the 1st meiotic division. They become polytenic and then reproduce to give rise to the polyploid macronucleus. The development of the macronucleus has been traced from a single diploid set of chromosomes and no evidence has been found for the formation of genetic “subnuclei.” During the early stages of the development of the macronuclear anlage, somatic pairing forces keep the homologs together, while in the later stages these forces cease to exert influence. While these changes are in progress the old macronucleus; breaks up into small irregular polymorphic bodies which are scattered throughout in the cytoplasm. The exconjugants usually encyst and the cysts are not favorable for detailed cytologic study.