SYNOPSIS 



CLASSIFICATION OF THE ANIMAL KINGDOM. 



SUB-KINGDOM (TYPE) L PROTOZOA. 



(Extinct forms are marked with an asterisk. ) 



ANIMALS composed of undifferentiated protoplasm, or, at 

 most, of protoplasm which is so far differentiated as to have 

 developed a consistent external layer or wall and a central 

 " nucleus " or " endoplast," the organism in the latter case 

 becoming a " cell" In the most typical Protozoa the organ- 

 ism remains unicellular, and in no case are definite " tissues " 

 developed by the differentiation of a primitive cellular aggre- 

 gate. No definite " body-cavity " is in any case developed. 

 There is no recognisable nervous system, and there is either 

 no differentiated alimentary apparatus, or, at most, a rudi- 

 mentary one. 



Most naturalists now divide the animal kingdom into the two primary 

 sections of the Protozoa and the Metazoa ; the former comprising animals 

 which are essentially unicellular, or consist of simple undifferentiated 

 masses of sarcode while the latter comprises animals which commence 

 their existence as single cells, but which ultimately form cellular aggre- 

 gates, certain of the cells composing them being differentiated so as to 



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