CHAP. XIV The Simplest Animals 215 



We must return, however, to the everyday life of the Protozoa. 

 Rhizopods move by means of outflowing processes of their hving 

 matter which stream out at one corner and are drawn in at another ; 

 the Infusorians move more rapidly by undulating flagella or by 

 numerous cilia which work like flexible oars ; the parasitic 

 Gregarines without any definite locomotor structures sometimes 

 writhe sluggishly. A few Infusorians have a spasmodic leaping or 

 springing motion, while the activity of others (like Vorticella) which 

 in adult life are fixed, is restricted to the contraction and expansion 

 of a stalk and to the action of cilia around the opening which serves 

 as a mouth. Arcella is aided in its movements by the formation of 

 gas bubbles in diflerent parts of its cell-substance. 



The food consists of other Protozoa, of minute Algas, and of 

 organic debris, simply engulfed by the Amoebae, wafted by cilia 

 into the "mouth" of most Infusorians. The parasitic Gregarines 

 absorb the debris of the cells or tissues of the animals in which they 

 live, while not a few suck the cell-contents of freshwater Algse like 

 Spirogyra. A few Protozoa are green, and some are able to use 

 carbonic acid after the manner of plants. Almost all Radiolarians 

 and a few Foraminifers live in constant and mutually helpful 

 partnership or symbiosis with small Algas which flourish within 

 their cell-substance. 



As to the other functions, the cells absorb oxygen and liberate 

 carbonic acid, digest the food-particles and excrete waste, produce 

 cysts or elaborate shells. 



6. Psychical Life of the Protozoa. — We linger over the 

 Protozoa because they illumine the beginnings of many activities, 

 and we cannot leave them without asking what light they cast upon 

 the conscious life of higher animals. Is the future quite hidden in 

 these simple organisms or are there hints of it ? 



According to some, the Protozoa, with frequently rapid and 

 useful movements, with capacities for finding food and avoiding 

 danger, with beautiful and intricate shells, are endowed with the 

 will and intelligence of higher forms of life. According to others, 

 their motions are arbitrary and without choice, they are only much 

 more complex than those of the potassium ball which darts about 

 on the surface of water, the organisms are drawn by their food 

 instead of finding it, their powers of selection are sublimed chemical 

 afiinities, their protective cysts are quite necessary results of partial 

 death, and their houses are but crystallisations. In both interpreta- 

 tions there is some truth, but the first credits the Protozoa with too 

 much, the second with too little. 



Cienkowski marvelled over the way in which Vanipyrella sought 

 and found a Spirogyra filament and proceeded to suck its contents ; 

 Engelmann emphasised the wonderful power of adjustment in Arcella 



