BY WILLIAM J. BYRAM. 



displays a very slow, gradual, diffluent movement, and keeps 

 putting forth parts of its substance in the form of protuberances 

 or processes. There you have the whole life-problem before you, 

 ere you have fairly realised that you are looking at anything at 

 all. That greyish-white, glairy, albuminous-looking patch is an 

 amoeba, a term which means " formless " ; and, as the name 

 implies, the amoeba is a shapeless speck quite invisible to the 

 naked eye. An insignificant speck truly, but a speck of a most 

 marvellous substance, protoplasm, which differs from all other 

 substances in having as one of its attributes life or rihiUtij. 

 Well has protoplasm been designated by the late Professor Huxley 

 " the physical basis of life," for whether in the protozoon, or 

 lowliest animal, in the protophyte or simplest plant, in a mush- 

 room, in a tree, in a worm, or in a man it is the seat of the 

 wonderful vital phenomena, and is the source and fount alike of 

 all the bewildering complexity of the organic world. We now 

 see that the understanding of Tennyson's little flower involves 

 the understanding of protoplasm ; and you might substitute for 

 the complex flowering plant our amojba and apply the poet's 

 apostrophe to it equally well. The amoeba, therefore, is of pro- 

 found interest to us as the type of the biological unit — the single 

 cell. Here, on using the term cell for the first time, we must get 

 a clear conception of what we mean. The term was brought 

 into prominence in the first half of the present century by two 

 German biologists (Schleiden and Schwann), and they both 

 defined the cell as a minute vesicle enclosing fluid contents, that 

 is to say, a small chamber or cellula, in the true sense of the 

 word. This conception is a good example of one of those half 

 truths which are often the first fruits of the scientific method. 

 The definition exactly describes the usual form of the plant cell, 

 and certain forms of animal cell ; but we now know many forms 

 of both the plant and animal cell in which the cell wall is 

 entirely wanting. The research of the past fifty years has 

 resulted in the modification of the idea of an enclosed vesicle ; 

 and although we still retain the term " cell " as a convenient 

 mode of referring to the biological unit, we associate with it the 

 modern definition, which simply declares that the cell is a 

 minute mass of protoplasm endowed with the attribute of life. 

 Looking at our amoeba again we see that the idea of a vesicle 

 cannot be applied to it, for it has no investing membrane. All 



