TYPES OF FERTILIZATION -

On the basis of site of fertilization, it is of two types - 1. External fertilization        2. Internal fertilization

1.       EXTERNAL FERTILIZATION -

When fertilization take place outside the body, mainly it occurs in water.

Both the sperm & ova are released simultaneously in the water.

External fertilization is two types -

(i) External fertilization in fresh water - Eg. fishes, amphibians & aquatic invertebrate animal.

(ii) External fertilization in sea water - This types of fertilization take place in lower animals.

2.       INTERNAL FERTILIZATION -

It take place generally oviduct of female. In urodela the internal fertilization take place in the lower part of the oviduct.

In Salamendra, reptiles, birds & mammals the internal fertilization take place in upper part of the oviduct.

In Ovo-viviparus & viviparus animals always internal fertilization take place.

In oviparous animals fertilization may be external or internal.

On the basis of sperm penetration, fertilization is of 2 types -

1.      MONOSPERMY -

When one sperm enter into an ovum is called as monospermy. It is most common type of fertilization.

2.      POLYSPERMY -

When two or more sperms enter into an ovum. It is 2 type -

(i) Pathological polyspermy - In this more than one sperm enter into immature and highly mature ova and all sperm participate to amphimixis. The resulting embryo is dead.

(ii) Physiologicla polyspermy -

In this many sperm are enter into the ova but only one sperm participate to amphimixis.

Eg. Molluscs, Insect, Elasmobranchi, Urodela, Reptiles, Birds & Rabbit. Dead sperms are called merozoites.