In the paddles of the gigantic extinct sea-lizards, and in the mouths of certain suctorial crustaceans, the general pattern seems thus to have become partially obscured.

There is another and equally curious branch of our subject; namely, serial homologies, or the comparison of the different parts or organs in the same individual, and not of the same parts or organs in different members of the same class.

Most physiologists believe that the bones of the skull are homologous--that is, correspond in number and in relative connexion--with the elemental parts of a certain number of vertebrae.