Some of the animal Monera acquired a nucleus, and became amoeba-like creatures; and, out of certain of these, ciliated infusorium-like animals were developed. These became modified into two stirpes: A, that of the worms; and B, that of the sponges. The latter by progressive modification gave rise to all the Coelenterata; the former to all other animals.

But the aged people and the children there's the difficulty. If I invite a man who possesses unquestionable qualifications, but has a large family, what am I to do? I can't crowd out others as desirable as he for the sake of carrying all of his stirpes. The principles of eugenics demand a wide field of selection."

It became a matter of doubt whether the heir per capita or the heir per stirpes was to succeed; but whether the heir per capita gave way when the heirdom per stirpes took place, or the Catholic heir when the Protestant was preferred, the inheritable principle survived with a sort of immortality through all transmigrations, Multosque per annos Stat fortuna domûs, et avi numerantur avorum.

But A soon broke up into two principal stirpes, of which one, a, became the root of the Annelida, Echinodermata, and Arthropoda, while the other, b, gave rise to the Polyzoa and Ascidioida, and produced the two remaining stirpes of the Vertebrata and the Mollusca.