Composite light micrographs of Oxytricha sp. reproducing via binary fission. There are three shots of asexual binary fission from top to bottom. During fission, the micronucleus undergoes mitosis and the macronucleus elongates and undergoes amitosis. The cell then divides in two, and each new cell obtains a copy of the micronucleus and the macronucleus. Darkfield illumination.