238 AMCRBA CHAP. 



structure accompanied by a division of physiological 

 labour becomes more and more marked, some cells 

 giving rise to organs of locomotion, others to organs of 

 reproduction, and so on. But every function necessary 

 for the life of an animal or a plant is due in the first 

 instance to protoplasm, and a simple cell, like the 

 Amoeba, can perform them all. 



In the next two chapters we shall study certain other 

 unicellular organisms which show an advance on 

 Amoeba in possessing a certain amount of morphological 

 and physiological differentiation. But the structural 

 differentiations, as they are merely parts of one cell, 

 cannot be spoken of as " organs " in the sense in which 

 we have used the word hitherto, as they are not com- 

 posed of numerous cells. They are, however, organs 

 in the physiological sense, as they perform different 

 functions. 



PRACTICAL DIRECTIONS 1 



Amoeba. 



Examine a drop of water from the bottom of a pond, with 

 the low power, first putting on a cover-glass, and look for 

 Amoebse : if the water does not contain small particles of 

 sand or mud, place a small piece of thin paper under the 

 edge of the cover so as to avoid crushing the organisms. 

 When you have found a specimen, note 



I. The irregular and changing form of the animal, the 

 protoplasm running out into blunt pseudopods. 



1 You should, if possible, try to obtain specimens of Amoebae 

 and the other fresh-water organisms described in this and the two 

 following chapters for yourself, by collecting stagnant pond-water, 

 together with a little of the mud at the bottom and some water- 

 weeds, and Siting it stand for a few days in a glass jar or bottle. 

 If you are unable to find the organisms you require, they, as 

 well as most of the other animals described in this book, may be 

 obtained from dealers in Natural History objects (see, e.g., the 

 advertisements in Nature). 



