(a) Syngamy involves the complete and permanent fusion of two haploid gametes to form a diploid zygote. It is the mode of sexual reproduction seen in animals.
(b) Different kinds of syngamy: 
Depending upon the degree of differentiation of the fusing gametes syngamy may be of following types. 
(i) Autogamy: :
The male and female gametes are produced by the same cell or same organism and both the gametes fuse together to form a zygote. e,g: Actinosphaerium and Paramecium. 
(ii) Exogamy:
The male and female gametes are produced by different parents and they fuse to form a zygote. So it is biparental. e,g: Human - dioecious or unisexual animal
(iii) Hologamy:
In lower organisms, sometimes the entire mature organisms do not form gametes but they themselves behave as gametes and the fusion of such mature individuals is known as hologamy. (e,g:) Trichonympha
(iv) Paedogamy:
Sexual union of young individuals produced immediately after the division of the adult parent cell by mitosis.
(v) Merogamy:
Fusion of small sized and morphologically different gametes (merogametes) takes place.
(iv) Isogamy:
The fusion of morphological and physiological identical gametes (isogametes). (e,g:) Monocystis
(vii) Anisogamy:
Fusion of dissimilar gametes. (e,g:) Higher invertebrates and all vertebrates

(i) Simple binary fission:
(i) The plane of division is hard to observe
(ii) The contractile vacuoles cease to function and disappear.
(iii) The nucleoli disintegrate and the nucleus divides mitotically.
(iv) The cell then constricts in the middle, so the cytoplasm divides and forms two daughter cells.

(ii) Multiple fission:
(i) During unfavourable conditions i.e., (increase or decrease in temperature, scarcity of food) Amoeba withdraws its pseudopodia and secretes a three-layered, protective, chitinous cyst wall around it.
(ii) After that it becomes inactive. This phenomenon is called encystment.
(iii) When conditions become favourable the encysted Amoeba divides by multiple fission and produces many minute daughter amoebae called pseudopodiospore or daughter amoebulae
(iv) The cyst wall absorbs water and breaks off to liberate the young pseudopodiospores, each with a fine pseudopodia.
(v) They feed and grow rapidly to lead an independent life.
(iii) Sporulation:
(i) During unfavourable conditions Amoeba multiplies by sporulation without encystment.
(ii) Nucleus breaks into several small fragments or chromatin blocks.
(iii) Each fragment develops a nuclear membrane becomes surrounded by cytoplasm and develops a spore-case around it.
(iv) When conditions become favourable, the parent body disintegrates and the spores are liberated, each develops into a young amoeba.

Binary Fission:
(a) The parent organism divides into two halves and each half forms a daughter individual.
(b) The nucleus divides first amitotically or mitotically (karyokinesis), followed by the division of cytoplasm (cytokinesis).
(c) The resultant offsprings are genetically identical to the parent.
(d) Depending on the plane of fission, binary fission is of the following types
(i) Simple irregular binary fission
(ii) Transverse binary fission
(iii) Longitudinal binary fission
(iv) Oblique binary fission
(i) Simple binary mission (e,g: Amoeba):
(i) It occurs in Amoeba like irregular shaped organisms.
(ii) The plane of division is hard to observe.
(iii) The contractile vacuoles cease to function and disappear.
(iv) The nucleoli disintegrate and the nucleus divides mitotically.
(v) The cell then constricts in the middle, so the cytoplasm divides and forms two daughter cells each with a single nucleus.
(ii) Transverse binary fission: (e,g:) Paramecium and Planaria
(i) The plane of the division runs along the transverse axis of the individual.
(ii) In Paramecium the macronucleus divides by amitosis and the micronucleus divides by mitosis.
(iii) Longitudinal binary fission: (e,g:) Vorticella and Euglena
(i) The nucleus and the cytoplasm divide in the longitudinal axis of the organism.
(ii) In flagellates, the flagellum is retained usually by one daughter cell.
(iii) The basal granule is divided into two and the new basal granule forms a flagellum in the other daughter individual.
(iv) Oblique binary fission: (e,g:) Ceratium
(i) The plane of division is oblique.
(ii) It is seen in dinoflagellates.

(a) Hologamy: In Hologamy, the adult individuals do not produce gametes, but they themselves act as gametes and fuse to form new individuals.
E.g: Trichonympha
(b) Isogamy: Fusion of morphologically & physiologically similar gametes.
E.g: Monocystis
(c) Anisogamy: Fusion of morphologically & physiologically dissimilar gametes.
Eg: Vertebrates.
(d) Merogamy: Fusion of small-sized morphologically different gametes (microgametes)
(e) Paedogamy: Fusion of young individuals produced immediately after the mitotic division of adult parent cell.

Regeneration is regrowth in the injured region. Regeneration was first studied in Hydra by Abraham Trembley in 1740. Regeneration is of two types, morphallaxis, and epimorphosis. In morphallaxis, the whole body grows from a small fragment e.g. Hydra and Planaria. When Hydra is accidentally cut into several pieces, each piece can regenerate the lost parts and develop into a whole new individual. The parts usually retain their original polarity, with oral ends, by developing tentacles .and aboral ends, by producing basal discs. Epimorphosis is the replacement of lost body parts. It is of two types, namely reparative and restorative regeneration. In reparative regeneration, only certain damaged tissue can be regenerated, whereas in restorative regeneration severed body parts can develop. e.g. starfish, the tail of wall lizard.

In binary fission, the parent organism divides into two halves and each half forms a daughter individual. The nucleus divides first amitotically or mitotically (karyokinesis), 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 is of the following types
(i) Simple irregular binary fission
(ii) Transverse binary fission
(iii) Longitudinal binary fission
(iv) Oblique binary fission
(i) Simple irregular binary fission is seen in Amoeba like irregular shaped organisms, where the plane of division is hard to observe. The contractile vacuoles cease to function and disappear. The nucleoli disintegrate and the nucleus divides mitotically. The cell then constricts in the middle, so the cytoplasm 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 the micronucleus divides by mitosis.

(iii) In Longitudinal binary fission the nucleus and the cytoplasm divides in the longitudinal axis of the organism. In flagellates, the flagellum is retained usually by one daughter cell. The basal granule is divided into two and the new basal granule 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 dinoflagellates. E.g. Ceratium.

(i) Development of an egg into a complete individual without fertilization is known as parthenogenesis.
(ii) It was first discovered by Charles Bonnet in 1745. Parthenogenesis is of two main types namely, natural Parthenogenesis and artificial Parthenogenesis.
(iii) In certain animals, parthenogenesis occurs regularly, constantly and naturally in their life cycle and is known as natural parthenogenesis.
Natural parthenogenesis are of different types:
a) Arrhenotoky: In this type only males are produced by parthenogenesis. E.g: honey bees
b) Thelytoky: In this type of parthenogenesis only females are produced by parthenogenesis E.g. Solenobia
c) Amphitoky: In this type parthenogenetic egg may develop into individuals of any sex. E.g: Aphis.
(iv) Natural parthenogenesis may be of two types, viz., complete and incomplete. Complete parthenogenesis is the only form of reproduction in certain animals and there is no biparental sexual reproduction. These are no male organisms and so, such individuals are represented by females only.
(v) Incomplete parthenogenesis is found in some animals in which both sexual reproduction and parthenogenesis occurs.
E.g. In honeybees; fertilized eggs (zygotes) develop into queen and workers, whereas unfertilized eggs develop into drones (male).
(vi) In paedogenetic parthenogenesis (paedogenesis) the larvae produce a new generation of larvae by parthenogenesis.
(vii) It occurs in the sporocysts and Redia larvae of liver fluke. It is also seen in the larvae of some insects. E.g. Gall fly.
(viii) In artifical parthenogenesis, the unfertilized egg (ovum) is induced to develop into a complete individual by physical or chemical stimuli. E.g. Annelid and seaurchin eggs.

(i) Regeneration is regrowth in the injured region. Regeneration was first studied in Hydra by Abraham Trembley in 1740.
(ii) Regeneration is of two types, morphallaxis and epimorphosis. In morphallaxis the whole body grows from a small fragment. E.g. Hydra and Planaria.
(iii) When Hydra is accidentally cut into several pieces, each piece can regenerate the lost parts and develop into a whole new individual.
(iv) The parts usually retain their original polarity, with oral ends, by developing tentacles and aboral ends, by producing basal discs.
(v) Epimorphosis is the replacement of lost body' parts. It is of two types, namely reparative and restorative regeneration.
(vi) In reparative regeneration, only certain damaged tissue can be regenerated, whereas in restorative regeneration several body parts can develop. E.g. star fish, tail of wall lizard.