Autogamy in Frontonia leucas (Ehrbg.)

Autogamy in Frontonia leucas is described for the first time. The process appears to occur at irregular intervals. From 7 to 10% of the individuals are affected. The beginning of autogamy is marked by a swelling of all the micronuclei which take part in the first two maturation divisions. The third division however affects only one of the second division products. Occasionally two or three may divide. A paroral cone is not prominent. But a small area close to the peristome is distinguishable as the region where the pronuclei fuse. The syn-karyon divides four times. Some of the division products disintegrate, after which 8 to 9 bodies are left which become differentiated into 4 to 5 macronuclear anlagen and 4 micro-nuclei. Mitotic division of the micronuclei results in their increase in number in the daughter individuals after metagamic divisions. Changes in the macronucleus during autogamy consist in its fragmentation and later absorption in the cytoplasm. There is some indirect evidence of a relationship between the dissolution of the old macronucleus and the development of the new.