LESSON XXVII 1 



THE GENERAL CHARACTERS OF THE HIGHER ANIMALS 



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, body-wall, enteron, stomodseum, procto- 

 dseum, ccelome, somatic and splanchnic mesoderm, are fairly 

 understood, all other points of structure become hardly more 

 than matters of detail. 



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

 the animal kingdom is divisible into seven primary sub- 

 divisions, called sub-kingdoms, types, or phyla. These are 

 as follows : 



Protozoa. Codenterata. 



Venues. Echinodermata. 



Arthropoda. Mollusca. 



Vertebrata 



Readers who have not studied zoology, or at least examined a series 

 of selected animal types, should omit this lesson and go on to the next. 



X 2 



