Light micrograph of two ciliate protozoans, Paramecium sp., undergoing conjugation, a type of sexual reproduction. The ciliates possess two different types of nucleus; a small diploid micro- nucleus & a larger polyploid macronucleus. During conjugation the cytoplasm of the two conjugants fuses, the macronuclei disintegrate and the micro- nuclei undergo meiotic division. The haploid products of this division are exchanged & a zygote nucleus is formed in both conjugants. New macro- nuclei are then formed by mitotic division of the genetic material of the new micronuclei. Magnification: x300 at 35mm size.