THE PRESENT POSITION OF THE CELL- 

 THEORY. 



(CONCLUSION.) 



THUS far I have tried to rehabilitate the cell as a vital 

 unit. I have now to deal with the further question as 

 to the part played by the cell in the composition of the higher 

 animals and plants. In the earlier part of this essay I 

 stated that Mr. Adam Sedgwick denied in toto the proposi- 

 tion that "the elementary parts of all tissues are composed 

 of cells ". Since writing those words, Mr. Sedgwick's reply 

 to my previously published criticisms has appeared, 1 and I 

 find that I have made a mistake. For he does not deny 

 the proposition, but says: ''The assertion that organisms 

 present a constitution which may be described as cellular is 

 not a theory at all ; it is — having first agreed as to the 

 meaning and use of the word cell — a statement of fact and 

 no more a theory than is the assertion that sunlight is com- 

 posed of all the colours of the spectrum ". I can only beg 

 Mr. Sedgwick's pardon. I certainly was led to suppose 

 from his earlier writings that he regards the cell as a 

 nonentity, in so far as it may be considered to be the 

 ultimate structural unit of the metazoa, and I recoiled from 

 his suggestion that the essence of development lay in "a multi- 

 plication of nuclei and a specialisation of tracts and vacuoles 

 in a continuous mass of vacuolated protoplasm ". 



Mr. Sedgwick now explains that he objects, not to the 

 statement that tissues are composed of cells — or, in his own 

 words, that they have a composition which may be described 

 as cellular — but to the statement that an individual meta- 

 zoon is an aggregate of lesser individuals, or, as it has often 

 been expressed, a cell colony or cell republic. I have else- 

 where — and as Mr. Sedgwick well says, after great effort — 

 come to agree with him on this point, for a careful survey 

 of a considerable range of facts led me to the conviction 



1 Adam Sedgwick, "Further Remarks on the Cell-Theory, with a Reply 

 to Mr. Bourne," Quart, four. Micr. Sci., vol. xxxviii., p. 331, 1895. 



