EIGHT BRANCHES OF THE ANIMAL KINGDOM. 15 
idea of the complicated relations between animals of differ. 
ent 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, Coelenterata, Vermes, Hchinodermata, Mol- 
lusca, Arthropoda, and Vertebrata. Their approximate 
relationships may be provisionally expressed by the follow- 
ing 
TABULAR VIEW OF THE E1aHT BRANCHES OF THE ANIMAL Kinapom. 
VIII. Vertebrata. 
Ascidians to Man. 
VIL. Arthropoda. 
Crustaceans and Insects. 
. VI. Mollusca. 
Clams, Snails, Cuttles. 
V. Echinodermata. 
Crinoids, Starfish, etc, 
| 
IV. Vermes. 
Worms, 
TIL. Celenterata. Il. Porifera. 
Hydra, Jelly-fishes. Sponges. 
J | 
METAzOA. 
Many-celled animals, with 3 cell-layers. 
I. Protozoa. 
Single-celled animals. 
It should be understood by the student that the classifi- 
cation presented in this book is a provisional one, based on 
cur present knowledge of the structure of the leading types 
