CIlAl^TKK XV 11 



THE MYSTERY OF THE CVAA. 



I HAVE already given a short aecount of the chemical composi- 

 tion of protoplasm — the hii!;hly complex snhstance now ln-M 

 to be the physical basis of life, and by one scIkjoI of biulorrists 

 alleged to explain, as a resnlt of that complexity, all the won- 

 drous phenomena of growth and development. 1 now propose 

 to give a very brief sketch of the physical characteristics of the 

 living cell, of its internal structure, and of the extraordinary 

 internal changes it undergoes during the growth or reproduc- 

 tion of all organisms. 



One of the lowest or most rudimentary forms of life is 

 the Amoeba, a living cell, just visible to the unaided eye as 

 a little speck of floating jelly. This creature, being one of 

 the most common of living microscopic objects, will have been 

 seen by most of my readers. At first, under a low microscopic 

 power, it appears structureless, as it was for some time de- 

 scribed to be, but with increasing power and perfection of the 

 microscope it is found to consist of three parts — a central 

 body of a nearly globular shape slightly darker and more 

 granular in texture, the outer jelly-like mass, and a small more 

 transparent globular portion, which looks like an air-bubble, 

 and is seen to undergo a slow motion of contraction and ex- 

 pansion; this is termed the "contractile vacuole,'' which, 

 when it has reached its full size, p(Thaps a quarter «»r a fifth 

 of the whole diameter, suddenly disappears, and after a little 

 while reappears and gradually grows again to it< maximum 

 size. The shape of the Amceba varies greatly. Sometimes it 

 is globular and immovable, but most fr':^quently it is very ir- 

 regTilar with arm-like processes jutting out in various direc- 

 tions. By careful watching, these are seen t-. increase or 



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