Animals multiply asexually by a number of methods like binary fission, multiple fission, budding, gem mules, fragmentation and spores or cysts.
(i) Binary Fission:
It is found in unicellular animals like amoeba, paramoecium, euglena, etc. After attaining an optimum size the adult individual undergoes a simple division into two daughter cells of equal size.
It consists of division of the nucleus followed by cleavage of cytoplasm into equal parts, each having a daughter nucleus. Binary fission can occur in any place in amoeba. It is longitudinal in euglena and transverse in paramecium.
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The organisms undergoing binary fission are almost immortal since they never grow old but divide to form two young offspring after attaining the adult size.
(ii) Multiple Fission:
The mode of asexual reproduction is found in unicellular animals or protozoan, e.g., amoeba, Plasmodium, monocyclic.
The nucleus of the parent cell undergoes repeated divisions to produce a number of daughter nuclei. The cytoplasm cleaves around each nucleus simultaneously to form a number of daughter cells or individuals inside a parent cell.
Ultimately, under favorable conditions parent cell membrane ruptures and daughter individuals are released. Sometime, the daughter cells derived from multiple fission develop resistant coverings to produce spores.