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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.
Perhaps the most startling proposition of all those which Professor Haeckel puts before us is that which he bases upon Kowalewsky's researches into the development of Amphioxus and of the Ascidioida, that the origin of the Vertebrata is to be sought in an Ascidioid form.
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