INTRODUCTION TO ZOOLOGY 



FIG. 1. Amoeba proteus. x 300. 

 nu, Nucleus ; ps, pseudopodium ; con. 



vac, contractile vacuole ; /. vac, 



food vacuoles. 



Structure When so magnified, it is seen as a round, or 

 more or less irregular, body, of a semi-fluid con- 

 sistency, the greater part of it being finely granular, whilst 

 round the mar-gin is a clear 



non - granular border. It is 

 colourless or slightly greyish 

 in tinge, but within the trans- 

 parent body can be seen various 

 opaque food particles which 

 have been absorbed. The body- 

 is continually changing its 

 shape, sending out a process 

 now in one direction, now in 

 another, or, if touched, with- 

 drawing all its processes, and 

 becoming round in outline. 



The substance of which 

 this body is formed is that 

 Protoplasm, of which Professor 

 Huxley wrote as " The Physi- 

 cal Basis of Life"; 1 for it is the substance which is present 

 in all living things, be they plant or animal, and which, so 

 far as we know, alone renders possible the phenomenon which 

 we call physical life. 



On carefully examining this protoplasmic body, two struc- 

 tures can usually be readily detected, embedded within it. There 

 is a small, oval or round, darker mass known as the nucleus 

 of the protoplasm. In chemical composition, this is very 

 similar to the rest of the living protoplasm, but it is denser, 

 and it performs special important functions within the cell, 

 controlling apparently the nutritive and reproductive processes. 

 Then, after a little search, a clear round space can also be 

 seen, which will disappear suddenly, and then slowly form 

 again, thus gaining the name of the contractile vacuole. When 

 visible, the space is filled with a watery fluid ; when the 

 vacuole contracts, this fluid is driven in radiating streams out 

 of the protoplasmic body. 



Such a mass of living protoplasm with its nucleus is known 

 as a cell, and Amoeba is therefore said to consist of one cell, 

 or to be unicellular. 



1 Lay Sermon in Collected Essays, vol. i. 



