Write notes on binary fission in animals.

Explanation

In binary fission, the parent organism divides into two halves and each half forms a daughter individual. The nucleus divides first amitotically or mitotically (karyokinnesis), followed by the division of the cytoplasm (cytokinesis). The resultant offsprings are genetically identical to the parent. Depending on the plane of fission, binary fission if of the following types
i. Simple irregular binary fission
(ii) Transverse binary fission
(iii) Longitudinal binary fission
(iv) Oblique binary fission.
(i) Simple binary fisssion is seen in Amoeba like irregular saped organism, where the plane of division is hard to observe. The contractile vacuoles cease to function and dissappear. The nucleoli disintegrate and the nucleus divides miotically. The cell then constricts in the middle, so the cytoplams divides and forms two daughter cells.

(ii) In transverse binary fission , the plane of the division runs along the transverse axis of the individual. E.g. Paramecium and Planaria. In paramecium the macronucleus divides by amitosis and teh micronucleus divide by mitosis.

(iii) In longitudinal binary fission, the nucleus and the cytoplasm divides in the logitudinal axis of the organism. In flagellates, the flagellum is retained usually by one daughter cell. Teh basal granule is divide into two and the new basal ranule forms a flagellum in the other daughter individual E.g. Vorticella and Euglena.
(iv) In oblique binary fission the plane of division is oblique. It is seen in dinofalgellates. E.g. Ceratium.