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.

The anterior and posterior limbs in all the higher vertebrate classes are plainly homologous.

So it is with the wonderfully complex jaws and legs of crustaceans.