MIGHT BRANCMES OF THE ANIMAL KINGDOM. 15 



idea of the complicated relations between animals of difEer-. 

 «nt groups. 



The Animal Kingdom may be divided primarily into 

 "two series of branches ; those for the most part composed 

 -of a single cell, represented by a single branch, the Proto- 

 zoa, and those whose bodies are composed of many cells 

 (Metazoa), the cells arranged in three fundamental cell- 

 layers — viz., the ectoderm, mesoderm, and endoderm. The 

 .series of Metazoa comprises the seven higher branches — i.e., 

 the Porifera, Gcelenterata, Ecliinodermata, Vermes, Mol- 

 iusca, Arthropoda, and Vertebrata. Their approximate 

 jelationships may be provisionally expressed by the follow- 

 ing 



Tabulab View op thb Eight Bbanches of the Animal Kingdom. 



Till. Vertebrata. 

 ^^cidians to Man. 



VII. Arthropoda. 

 Crustaceans and Insects. 



VI. Molluaca. 

 Clams, Snails, Cuttles. 



V. Vermes. 

 Flat and Round Worms, Polyzoa, 

 Brachiopods, Annelids. 



3V. Ecliinodermata. 

 Crinolds, Starfish, etc. 



III. Calenterata. 

 Hydra, Jelly-fishes. 



II. Porifera. 



Sponges. 



Mbtazoa. 

 Many-celled animals, with 3 cell-layers. 



I. Protozoa. 



Single-celled animals. 



It should be understood by the student that the classifl- 

 «ation presented in this book is a provisional one, based on 

 Crur present knowledge of the structure of the leading types 



