I AMOEBA II 



consists entirely of cytoplasm while the other possesses in addition a 

 nucleus. Subsequent observation shows that this difference as regards 

 the possession of a nucleus is accompanied by striking differences in 

 behaviour. The nucleated portion continues its existence as a perfectly 

 normal Amoeba, performing all the vital functions — moving, feeding, 

 growing, exactly as did the original individual. 



The non-nucleated portion may for a little seem to behave much as 

 the other. It may push out pseudopodia ; if it does not contain the 

 original contractile vacuole it may form a new one. But its movements 

 are sluggish. It is unable to creep along a solid surface and investigation 

 shows this to be correlated with its being no longer able to form the thin 

 coating of slime which normally covers its surface. Again it may ingest 

 food particles but these are no longer properly digested — the power of 

 secreting the digestive ferments is apparently no longer present. Gradu- 

 ally its activities diminish and within a week or ten days they come to 

 an end in death. 



General Remarks on Amoeba 



Having summarized the main facts regarding Amoeba it will now be 

 convenient to glance back at these facts and see what general lessons 

 are to be learned from them. 



Firstly we see that the facts fall into two main categories — facts of 

 structure and facts of living activity or function. These two categories 

 constitute the two primary subdivisions of zoological science : Anatomy, 

 which deals with all details of structure, form, etc. — such details in fact 

 as can be gathered from the investigation of the dead body — and 

 Physiology, which concerns itself with all the various manifestations of life. 



Secondly Amoeba provides us with a good example illustrating the 

 conception of what is known as a cell — a conception which permeates 

 all biological science. A cell is " a mass of . protoplasm containing a 

 nucleus." An Amoeba consists of a single cell while the body of any of 

 the larger animals is composed of vast numbers of cells derived by fission 

 repeated over and over again from a single original cell — the egg. The 

 cell does not merely enclose the nucleus but while alive its activities 

 are to a great extent controlled by the nucleus. This again is illustrated 

 by Amoeba for we have seen how the removal of the nucleus not only 

 stops some of the striking activities of the Amoeba but after a short time 

 renders life itself impossible. 



A further point of importance emerges from the experiment in which 

 the Amoeba is cut in two. Careful and continued scrutiny of the 

 nucleated portion shows that its nucleus undergoes a gradual diminution 



