Excerpt from A Text-Book of Zoology, Vol. 2 of 2 IN the arrangement which it has been found convenient to follow in the present work, the Vertebrate animals (fishes, Amphibians, Reptiles, Birds, and Mammals), together with the Cephalochorda or Lancelets, the Urochorda or Ascidians, and the Hemichorda or Balanoglossus and its allies, are all grouped together in a single phylum - the Chordata. The main groups comprised in this assemblage, however, differ so widely from one another' in certain essential points, and the common features uniting them together are so few, that it has been thought advisable to depart from the plan of arrangement followed in connection with the rest of the phyla, and to make a primary division in this case not into classes, but into sub-phyla. In accordance with this scheme the phylum Chordata is regarded as made up of three sdb-phyla - the Hemichorda, the Urochorda, and the Euchorda, the last-mentioned comprising the two sections Acrania and Craniata or Vertebrate, each of which receives separate treatment. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.