Ovipary, Vivipary and Ovovivipary

In each case of external and in some cases of internal fertilisation, development of the fertilized egg (zygote) occurs outside the mother's body. The egg is laid either in water or in soil, on plants, or in the body of their hosts in case of specific parasites. Ail such animals or called oviparous (laying eggs). A number of exceptional cases of non-chordates showing, vivipary that is giving birth to young ones nourished by the genital tracts of the female, are found in some insects like tsetse fly (Glossina). A third condition is that of Ovovivipary. In this case, after fertilisation the zygote is retained in the female reproductive system with no any direct connection with the maternal tissues for providing nourishment. Here it undergoes development. Finally the eggs hatch still inside the female and the young ones are "born". This happens for instance in certain flies.