238 AMCEBA CHAP. 



the development of the frog from the unicellular oosperm 

 (p. 206) that a differentiation oj 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 physio- 

 logical 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 composed 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 Amcebre : if the water 

 does not contain small particles of sand or mud, place a small piece of 

 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 and 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 letting 

 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']. 



