Knowledge of the natural relationships and ancestral
history of animals can only be gained by a comparative study of their parts
(Comparative Anatomy) and of their mode of development (Embryology or
Ontogeny). In addition to existing animals, fossil forms must also be taken
into consideration (Paleontology), and by combining the results obtained under
these three fields, it is possible to make an attempt to trace out the development
of the various species or groups in time (Phylogeny). As the different phases
of development of the species may be repeated to a greater or less extent in
those of the individual, the fields of Phylogeny and Ontogeny help to complete
one another. Therefore, Comparative anatomy is a tool to the fields of
Phylogeny, Ontogeny, Homology, Anology and Homoplasy.
