222 



THE STUDY OF ANIMAL LIFE CHAP. 



matter spreads out in thick or thin, stiff or plastic, free or 

 interlacing processes, which often admit of a slow gliding 

 motion, and are still 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 general name of Rhizo- 



pods. In contrast to 

 the two preceding 

 types which have de- 

 finite boundaries or 

 "skins," the Rhizo- 

 pods are naked, and 

 their living matter 

 may overflow 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 Grega- 

 rines, often wrapped 

 up within a sheath, 

 we may call predomi- 

 nantly encysted ; 

 while those forms 

 which are inter- 

 mediate between these 

 two extremes, and 

 exhibit outflowing processes 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. 

 As the three phases represent the three physiological 

 possibilities of cell-life, it is natural to find that the very 



FIG. 61. A FORAMINIFER (Polyslomella 

 striyillala) WITH INTERLACING PRO- 

 CESSES OF THE LIVING MATTER FLOW- 

 ING OUT ON ALL SIDES. MAGNIFIED 

 FIFTEEN TIMES. 



(From Chambers's Encijclop. ; after 

 Max Schultze.) 



