THE PROTOZOA THE DAWN OF LIFE 3 



Greeks. Under the microscope the Amoeba looks like a tiny, semi- 

 transparent jelly-speck, about ^ inch in diameter, composed 

 of a soft, slimy, semi-fluid substance in which can be seen a 

 slightly denser globular body called the nucleus, the whole 

 organism being very irregular and varying in shape, changing 

 ever as we watch it, becoming round, oval, oblong, or lobed like 

 a distorted hand changes effected by the streaming of its proto- 

 plasm and the pushing out and withdrawal of blunt finger-like 

 processes. As we watch the expansion and contraction of these 

 finger-like processes, we shall see that as a result of their move- 

 ments the whole mass of the Amoeba is slowly drawn along, with 

 a curious streaming sort of motion. 



The Amoeba may contract its finger-like expansions and come 

 to a pause in its progress, and assuming a globular shape, secrete 

 a thick, almost shell-like coat, probably composed of some nitro- 

 genous substance, which completely envelops it, forming a cyst 

 or cell-wall. The formation of this enveloping cyst is of very great 

 importance to the Amoeba. Protected by its horny case, it 

 is enabled to survive periods of drought should the pond 

 dry up during the summer months. When the rains of autumn 

 replenish the pond, and conditions suitable for its active life are 

 once more restored, the Amoeba ruptures the cell-wall and makes 

 its escape. 



The Amoeba moves continually in all directions, its constantly 

 changing finger-like processes being merely temporary projections 

 of its semi-fluid body, and not special organs in the anatomical 

 sense for producing movements ; hence the reason for their being 

 called " pseudopodia," or " false-feet." 



The jelly-like, somewhat granular substance called proto- 

 plasm, 1 of which the Amoeba is composed, appears surrounded by 

 an outer glassy-looking and extremely thin pellicle or layer. 2 In 

 the interior mass of protoplasm may be made out the denser and 

 small rounded body of the nucleus, which does not alter in form 

 during the changes of shape which the Amoeba undergoes as a 

 whole. This nucleus consists of material closely resembling the 



1 From the Greek, protos, first ; plasma, a formation, from plasso, I shape or 

 moxild. The simplest life-matter known, and present in the tissues of both plants 

 and animate. 



2 The glassy outer portion is called by some observers the ectoplasm ; the denser 

 mass being called, in contradistinction, the tndoplasnt. 



