EMBRYOLOGICAL EVIDENCES -

• A comparative study of embryology of different groups of animals reveals certain features that provide evidences for organic evolution.
• There are striking similarities among the different species of invertebrates that have a sequence of embryonic developments.
• These similarities are as follows:

(i) Gill clefts and notochord appear on the embryonic development of all vertebrates from fishes to mammals. (ii) The notochord is replaced by the vertebral column in all adult vertebrates.

(iii) Lungs in adult amphibians, reptiles and mammals replace gills.

• The embryonic evidences can be taken into consideration on the basis of the following facts -

(i) Similarly in early development: In all the multicellular animals the fertilized egg (zygote) under goes cleavage to produce morula (solid mass of cells), blastula (a single layered hollow structure) & gastrula.

(ii) Resemblance in vertebrate embryos: The embryos of all vertebrates resemble one another.

(iii) Heart of a mammal or bird is initially two - chambered as in fished and finally becomes four-chambered. (iv) Tadpole of frog resembles to fish shows "ontogeny repeats phylogeny".

Tadpole of frog