310 SCIENCE PROGRESS. 



classification of the facts. Such a classification has yet to 

 be made. So long as a theory is dominant, as the cell- 

 republic theory was, exceptions and difficulties are glossed 

 over, or are explained away by a phrase. When I made a 

 vigorous onslaught on Mr. Sedgwick, I was afraid that he 

 wished to substitute King Stork for King Log and bring us 

 under the domination of a new theory of his own. His 

 reply to my strictures and his careful exposition of his own 

 standpoint are reassuring on this point, and if I exceeded the 

 limits of courtesy in my article, I did so under a misunder- 

 standing and express my regret for it. Mr. Sedgwick has 

 done a great service in breaking the bonds of the old theory. 

 Now the question is, having got our liberty, what are we 

 going to do with it ? 



Firstly, I think, we have got to make up our minds as 

 to what we mean by a vital unit. 



In the first part of this essay I stated that the cell is par 

 excellence the vital unit, by which I meant nothing more 

 than that it is the simplest form of material aggregate in 

 which individual life is possible. There would seem to be 

 no objection to such an application of the word unit. But 

 the term unit is a relative one, and its correlative is 

 multiple. If, therefore, we see that the developing embryoes 

 of many animals and likewise the tissues of the adult forms 

 are made up of structures which we must call cells, and if 

 we call the cell a vital unit, we are obliged to conclude that 

 the animals in question are composed of an aggregate of 

 vital units, which leads us directly to the doctrine of a cell- 

 republic. Thus at the outset we are confronted by the 

 great difficulty that what experience teaches us to deny 

 reason compels us to affirm. 



There must be a flaw somewhere, either in the facts or 

 in the reasoning. There can hardly be any doubt about 

 the facts ; the flaw therefore must be in the reasoning, and 

 I do not doubt that it consists in our insistence on applying 

 the idea of a unit to biological facts. As Whewell would 

 have said, the idea is inappropriate. The term unit, as we 

 use it in Biology, conveys a double meaning. On the one 

 hand, it borrows part of its meaning from the idea of num- 



