CYTOLOGY OF CONJUGATION IN PARAMECIUM MULTIMICRONUCLEATUM, SYNGEN 2, STOCK II.

Abstract

SYNOPSIS. Studies at successive stages were made to provide a basis for genetic work and to reexamine some unique features in Landis' account. All micronuclei undergo two prezygotic divisions (meiotic), but only the nucleus in the paroral cone in each animal undergoes the third division (mitotic) yielding the male and female pronuclei. Double fertilization results from each mal pronucleus migrating to fuse with a stationary female pronucleus. During the three postzygotic nuclear divisions the conjugants separate. The eight nuclear products in each exconjugant differentiate into four macronuclear anlagen and four micronuclei. The micronuclei divide at each cell division; the macronuclear anlagen are segregated normally two to each fission product of the first cell division and one to each of the second fission products. Thereafter these new macronuclei divide (amitotically) at each cell division. The original macronucleus spins out and fragments. These pieces of the old macronucleus are passively segregated at each cell division. The unique features reported by Landis are not found in stock 11. Genetic implications are that following cross‐fertilization, the two exconjugant clones should be identical in phenotype for traits under direct genic control. Any trait, however, under the control of differently determined macronuclei should follow the segregation of the macronuclear anlagen at the second cell division.