212 



The Study of Animal Life vkkt ni 



more useful in surrounding minute food particles. To these root- 

 like processes, which are capable of very considerable, often almost 



constant, change, these 

 Protozoa owe their gen- 

 eral name of Rhizopods. 

 In contrast to tlie two 

 preceding types which 

 have definite boundaries 

 or "skins," the Rhizo- 

 pods are naked, and their 

 living matter may over- 

 flow at any point. 



As the Infusorians 

 are for the most part 

 provided with cilia from 

 which flagella differ only 

 in detail, we may speak 

 of the type as ciliated ; 

 the self-contained Gre- 

 garines, often wrapped 

 up within a sheath, we 

 may call predominantly 

 encysted ; while those 

 forms which are inter- 

 mediate between these 

 two extremes, and ex- 

 hibit outflowing pro- 

 cesses of living matter, 

 are called amoeboid in 

 reference to their most familiar type, the common Amoeba. • 



But though the members of each class are characterised by the 

 predominance of one of the three phases of cell-life, they sometimes 

 pass from one phase to another. Thus the ciliated or the amoeboid 

 units may become encysted. 



'\ ''^%\%~^ 



Fig. 40. — .\ ior:Lm\mkr {PolysiODiella sir! ffiiinta) 

 with interlacing processes of the living matter 

 flowing out on all sides. Magnified 10 times. 

 (From Chambers's Encycloji. ; after Max 

 Schultze.) 



Fig. 41.— Protomyxa. i, encysted ; 2, dividing into many units; 3, these escap- 

 ing as flagellate cells ; 4, sinking intu an amoeboid phase ; 5, fusing into a 

 Plasmodium. (From Chambers's ETicyclop. ; after Haeckel.) 



As the three phases represent the three physiological possibilities 



