VITAL FUNCTIONS. 79 



discharging all the vital functions ; but it is noticeable that 

 this is the lowest step in the ladder of life to which any veget- 

 able descends. A cell is an organised structure, and no 

 adult plants appear to possess the power of discharging all 

 the vital functions with a less amount of vital machinery 

 than this. In animals, however, as already remarked, we 

 meet with forms which, from a purely morphological point 

 of view, are certainly below the lowest plants. The Afofiera 

 of Haeckel, and the Fora7?iinifera^ discharge their vital func- 

 tions wholly through the medium of structureless albumi- 

 nous matter or *' bioplasm," which is destitute of a proper 

 wall, and never has definite structures developed in it. It 

 may be that the matter of life is in these creatures of a 

 higher grade than it is in the lower plants, but there is no 

 direct evidence which would support this view. It is cer- 

 tain, however, that there is a radical difference between the 

 living matter of an animal, such as one of the Foraminifcra^ 

 and a plant, such as a cell of yeast, since both discharge 

 functions of a radically different nature ; but there is no 

 ground for supposing that this difference is one of chemical 

 composition or physical character. We can also readily 

 see that the vital processes of one of the Foramviifera differ 

 so far from those of a plant, especially as regards the in- 

 gestion of food, that the structure of the vegetable cell 

 would be obviously unsuited to the higher organism. 



In the higher animals and plants we are presented with 

 structures which may be regarded as essentially aggregates 

 of cells; and there is now a "physiological division of 

 labour," some of the cells being concerned with the nutri- 

 tion of the organism, whilst others are set apart and dedi- 

 cated to the function of reproduction. Every cell in such 

 an aggregate leads a life which in a certain limited sense 

 may be said to be independent, and each discharges its own 

 function in the general economy. Each cell has a period 

 of development, growth, and active life, and each ultimately 

 perishes ; the Hfe of the organism not only riot depending 



