14 THE PROTOZOA THE DAWN OF LIFE 



The result of this irritant activity of warring life within the cells 

 is to attract greater supplies of available food materials, so that 

 the growth of the cells becomes abnormally accelerated, producing 

 a monstrous growth. The increased supplies of food material 

 benefit the Amcebulae at the expense of the cell-contents of the 

 host -plant, and after a time neighbouring Amcebulae fuse together 

 and plasmodium-formation begins. The plasmodia so formed are 

 capable of passing slowly from one cell to another, devouring 

 their contents and increasing in size, while the ravaged tissues 

 of the host-plant begin to disintegrate. Finally the plasmodia 

 break up into extremely minute particles of protoplasm, which 

 form into spherical spores. 



The Mycetozoa l comprise a group of simple organisms now 

 generally looked upon as primitive Protozoa, though at one time 

 claimed by botanists as fungi, and chiefly of interest to the bio- 

 logist. They are to be found living as composite, multinucleate 2 

 plasmodia upon the damp, mouldering walls of ancient cellars, 

 upon rotting timber, the decaying haulms of beans, and similar vege- 

 table matter, feeding upon the organic debris ; while one, called 

 Fuligo varians, or " Flowers of tan," is a large and conspicuous 

 species inhabiting tan-pits, where it is sometimes a great pest. 



The composite plasmodia are formed by the complete fusion of 

 numerous units, or, in a few rare cases, by their close contact with 

 each other. The margins of these plasmodia masses exhibit 

 amoeboid movements, slowly streaming out towards food 

 particles and engulfing them, spreading out towards moisture 

 and warmth, but withdrawing from concentrated light. A dor- 

 mant encysted stage sets in as a result of scarcity of food, lack 

 of moisture, or cold, enabling the organism as a resting spore pro- 

 tected by a surrounding cyst-wall to await the return of favour- 

 able conditions for renewed growth and activity. On the rup- 

 ture of the cyst-wall, a swarm spore, which generally possesses a 

 whip-like flagellum, makes its escape, and always eventually 

 loses the flagellum, becoming like a little Amoeba in appearance 

 and habit ; and in the uniting of these minute Amoebae we have 

 the formation of the composite plasmodia. 



The Sporozoa are a class of the Protozoa to which in only 



1 Greek, myces, a fungus ; zoon, an animal. 

 * Multinucleate, having many nuclei. 



