constantly developing into more and more complicated conditions owing to the bringing of its parts into new relations?  To answer these questions experimenters have been engaged in dividing developing eggs into pieces to determine what powers are still possessed by the fragments.  The results of such experiments are as yet rather conflicting, but it is evident enough from them that we can no longer look upon the egg cell as a simple undifferentiated cell.  In some way it already contains the characters of the adult, and when we remember that the characters of the adult which are to be developed from the egg are already determined, even to many minute details—­such, for instance, as the inheritance of a congenital mark—­it becomes evident that the egg is a body of extraordinary complexity.  And yet the egg is nothing more than a single cell agreeing with other cells in all its general characters.  It is clear, then, that we must look upon organization as something superior to cells and something existing within them, or at least within the egg cell, and controlling its development.  We are forced to believe, further, that there may be as important differences between two cells as there are between two adult animals or plants.  In some way there must be concealed within the two cells which constitute the egg of the starfish and the man differences which correspond to the differences between the starfish and the man.  Organization, in other words, is superior to cell structure, and the cell itself is an organization of smaller units.

As the result of these various considerations there has been, in recent years, something of a reaction against the cell doctrine as formerly held.  While the study of cells is still regarded as the key to the interpretation of life phenomena, biologists are seeing more and more clearly that they must look deeper than simple cell structure for their explanation of the life processes.  While the study of cells has thrown an immense amount of light upon life, we seem hardly nearer the centre of the problem than we were before the beginning of the series of discoveries inaugurated by the formulation of the doctrine of protoplasm.

==Fundamental Vital Activities as Located in Cells.==—­We are now in position to ask whether our knowledge of cells has aided us in finding an explanation of the fundamental vital actions to which, as we have seen, life processes are to be reduced.  The four properties of irritability, contractibility, assimilation, and reproduction, belong to these vital units—­the cells, and it is these properties which we are trying to trace to their source as a foundation of vital activity.