THE PRESENT POSITION OF THE CELL- 

 THEORY. 



PART I. 



A FEW years ago a discussion of the cell-theory would 

 have seemed superfluous. To-day, partly because 

 of criticisms which have been directed against the theory, 

 partly because of the great increase of our knowledge re- 

 specting cell-structure, the advantage and even the necessity 

 of such a discussion will be admitted by everybody who has 

 read and reflected on the subject. In what follows, I 

 propose to examine the cell-theory in the light of recent 

 criticisms and researches. I set out with the intention of 

 avoiding anything in the shape of polemical writing, but I 

 fear that I have in places fallen away considerably from the 

 course which I had proposed. In a much disputed subject 

 controversv is inevitable, a circumstance which need not be 

 regretted, for controversy is the whetstone of argument, and 

 obliges those who engage in it to be doubly careful both of 

 their facts and of the language in which they express them. 

 My antagonists will, I hope, give me the credit of the 

 desire to deal fairly with their arguments and criticisms, and 

 will acquit me of unnecessary bitterness. It has been my 

 object to elucidate the subject in hand rather than to try to 

 gain a dialectical advantage. 



It is advisable, before entering on the examination, to 

 have a clear conception of what the cell-theory really is. 

 This is the more necessary because one of its most recent 

 critics, Mr. Adam Sedgwick, has complained than nobody 

 will define the theory in an exact manner ; it is, he says, a 

 kind of phantom which takes different forms in different 

 men's eyes. I have shown in another place that this state- 

 ment is hardly fair, because there are some authors whose 

 researches on cytology entitle them to speak with authority 

 who have recently defined the cell-theory in a very precise 

 manner, though it may be conceded that there are biologists 



