This free living protozoa reproduces by asexual and sexual methods. In Paremoecium, the asexual reproduction is caused by transverse binary fission.
Binary Fission: Just before division the animal ceases feeding, the central portion of the body bulges. Micronucleus increases in size and fine spindle fibres are formed. Chromosomes divide eumitotically passing through all the stages of mitosis and each part goes to opposite pole. The macronucleus divides amitotically. One part of each of macronucleus and the micronucleus with the chromosome set go to the anterior part while the other goes to the posterior part. By this time a furrow appears at the centre at right angle to the orientation of the spindle. This furrow deepens into sharp constrictions which cut the animal into two in the transverse plane.
The oral groove or cytopharynx is inherited by the daughter at the anterior end. Regeneration of lost parts takes place in both of them. Two paramoecia develop from one parent by transverse binary fission.
Asexual reproduction in Paramoecium depends on-
(i) Temperature of water.
(ii) Quality and quantity of food.
Significance of binary fission
All the daughter paramoecia produced from the same parent have the same genetical constitution and so they form a clone.