LESSON XXVI 



THE CHIEF DIVISIONS OF THP: ANIMAL KINGDOM : THE 

 STARFISH 



The student who has once thoroughly grasped the facts of 

 structure of such typical unicellular animals as Amoeba and 

 the Infusoria, of such typical diploblastic animals as Hydra 

 and Bougainvillea, and of such a typical triploblastic animal 

 as Polygordius, ought to have no difficulty in understanding 

 the general features of the organization of any other members 

 of the animal kingdom. When once the notions of a cell, a 

 cell-layer, a tissue, an organ, body-wall, enteron, stomodseum, 

 proctodzeum, coelome, somatic and splanchnic mesoderm, 

 are fairly understood, all other points of structure become 

 hardly more than matters ot detail. 



If we turn to a text-book of Zoology we shall find that 

 the animal kingdom is roughly divisible into eight primary 

 sub-divisions, called sub-kingdoms, types, or phyla, 'i'hese 

 are as follows : — 



Protozoa. Echinodermata. 



Porifera, Arthropoda. 



Ca'Ienierata. Mollusca. 



" Vermes. ^^ Vertebraia. 



