Vertebrate Reproductive Methods

The five vertebrate classes exhibit reproductive methods that range from

• External fertilization to internal fertilization; and 

• Oviparity to viviparity.

External and internal fertilization

During external fertilization, the female vertebrate lays egg into the surrounding water and the male ejects sperms over them. The eggs which are fertilized by the sperms develop into young outside the female body. These developing young or embryos use the stored stored in the eggs for their development.

    In some vertebrates, the eggs remain in the female body. The male placed the sperms inside the body of the female through the reproductive opening. Fertilization occurs inside the body of the female. This is known as internal fertilization.

     Note : fishes , amphibians, reptiles and birds have a common opening to the exterior, called the cloaca, for that alimentary canal and the reproductive and urinary systems. Mammals usually have an opening for the alimentary canal, called the anus, and a common urinogenital opening for the reproductive and urinary systems.

     during external fertilization, a large number of eggs is laid since the chances of the eggs becoming fertilized and serving without being eaten by other animals are very small. This problems does not exist when fertilization is internal, so the female only produces a smaller number of eggs. Hence, external fertilization is wasteful while internal fertilization is economical.

 Oviparity , ovoviviparity and viviparity 

In oviparity, eggs are shed into the external environ where the embryos complete their development and hatch out of the eggs as young. The eggs may be unfertilized when they are shed as in most fished and amphibians or fertilized as in reptiles and birds.

     In ovoviviparity, the fertilized eggs are retained in the female body where the embryos develop using the stored food in the eggs. When fully developed, the young hatch from the eggs and are released from the female body. Certain fishes and reptiles are ovoviviparous.

   In viviparity, the young develop inside the female body, obtaining nourishment directly from the female parent. When fully developed, the young are born alive. A few fishes and Rep, and practically all mammals are viviparous.

      Note: Most invertebrates are oviparous. Some are ovoviviparous and a few are viviparous.