THE PRESENT POSITION OF CELL-THEORY. 99 



criticisms, and partly with the much more weighty argu- 

 ments brought forward at the same time by Dr. Oscar 

 Hertwig, says that my criticisms, in so far as they are 

 directed against the inadequacy of the cell-theory of develop- 

 ment, are largely the result of misunderstanding ; this may 

 in part be true, but I cannot have misunderstood the simple 

 meaning of his first paragraph, and I wish to insist on the 

 fact that the cell-theory, as it was promulgated by Schwann, 

 did not regard cell-formation as the whole secret of organic 

 development, and that the cell was not, in the mind of the 

 author of the cell-theory, the alpha and omega of both 

 morphological and physiological research in the animal 

 kingdom. If this is clearly understood at the outset, it will 

 help to remove much possible misunderstanding. 



But, as Mr. Sedgwick has rightly said, we have to deal 

 not only with what its authors thought, but with the cell- 

 theory as it is understood and taught at the present day. 

 I have already pointed out * that the most recent definition 

 of the cell-theory is, to all intents and purposes, identical 

 with the broader generalisations of Schwann. Dr. Oscar 

 Hertwig writes : 2 " Animals and plants, so dissimilar in their 

 outward appearances, are similar in the essentials of their 

 anatomical structure, since both are composed of similar 

 elementary parts which for the most part are only recognis- 

 able by the microscope. . . . Since the cells, into which 

 the anatomist resolves vegetable and animal organisms, are 

 the bearers of the vital processes, they are, as Virchow has 

 expressed himself, the vital units. Viewed from this stand- 

 point the whole life process of a composite organism appears 

 to be nothing else than the extremely complicated result of 

 the individual life processes of its numerous and variously 

 functional cells." This is simply a restatement in other 

 words of two of the fundamental principles of Schwann, 

 namely (1) that the elementary parts of all tissues are formed 



1 G. C. Bourne, "A Criticism of the Cell-theory," Quart. Jour. Micr. 

 Science, vol. xxxviii., p. 137, 1895. 



2 O. Hertwig, Die Zelle utid die Gewebe. Berlin : R. Friedlander 

 und Sohn, 1893. 



