130 



PHYLUM PROTOZOA — THE SIMPLEST ANIMALS 



■possibilities: (a) the amoeboid units, neither very active nor very 

 passive, form a median compromise ; {b) the ciHated Infusorians, which 

 are usually smaller, show the result of a relative predominance of ex- 

 penditure ; (c) the encysted Gregarines represent an extreme of 

 sluggish passivity. 



But, as Geddes and others have shown, the cells of a higher animal 

 often pass from one phase to another — the young amoeboid ovum 

 accumulating yolk becomes encysted, the ciliated cells of the windpipe 

 may, to our discomfort, sink into amoeboid forms. The same is true of 



CORTICATA.) 



Predominantly 

 ciliated and 



active. 

 Infusorians. 



Classification of Protozoa 



(GVMNOMYXA.) 



Predominantly 

 amoeboid. 



Rhizopods. 



(CORTICATA.) 



Predominantly 

 encysted and 



passive. 

 Sporozoa. 



ACINETARIA. 



RADIOLARIA. 



CILTATA. 

 Rhynchoflagellata. 



DiNOFLAGELLATA. 



FLAGELLATA. 



FORAMINIFERA. 



Labyrinthulidea. 



Heliozoa. 



LOBOSA. 



SPOROZOA 



OR 



GREGARINES. 



Proteomyxa and Mycetozoa. 

 Primitive Forms. 



the Protozoa ; thus in various conditions the ciliated or flagellate unit 

 may become encysted or amoeboid, while in some of the simplest forms, 

 such as Proiomyxa, there is a " cell-cycle " in which all the phases occur 

 in one life-history. 



Systematic Survey 



A. Primitive forms.— Under this heading may be included two 

 classes : I ) the Proteomyxa, primitive, insufficiently known forms often 

 without a nucleus, though nuclear material may be present in the form 



