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.