IV] OF THE CELL-THEORY 343 



apparently all its later steps can be carried on, independently of 

 nuclear action. Nor, as Verworn pointed out, can the nucleus 

 possibly be regarded as the "sole vehicle of inheritance," since only 

 in the conjunction of cell and nucleus do we find the essentials of 

 cell-hfe. "Kern und Protoplasma sind nur vereint lebensfahig," as 

 Nussbaum said. Indeed we may, with E. B. Wilson, go further, 

 and say that "the terms 'nucleus' and 'cell-body' should probably 

 be regarded as only topographical expressions denoting two 

 differentiated areas in a common structural basis." 



Endless discussion has taken place regarding the centrosome, 

 some holding that it is a specific and essential structure, a permanent 

 corpuscle derived from a similar pre-existing corpuscle, a "fertilising 

 element" in the spermatozoon, a special "organ of cell-division," 

 a material "dynamic centre" of the cell (as Van Beneden and 

 Boveri call it); while on the other hand, it is pointed out that 

 many cells live and multiply without any visible centrosomes, that 

 a centrosome may disappear and be created anew, and even that 

 under artificial conditions abnormal chemical stimuh may lead to 

 the formation of new centrosomes. We may safely take it that the 

 centrosome, or the "attraction sphere," is essentially a "centre of 

 force," and that this dynamic centre may or may not be constituted 

 by (but will be very apt to produce) a concrete and visible con- 

 centration of matter. 



It is far from correct to say, as is often done, that the cell- wall, 

 or cell-membrane, belongs "to the passive products of protoplasm 

 rather than to the hving cell itself"; or to say that in the animal 

 cell, the cell-wall, because it is "slightly developed," is relatively 

 unimportant compared with the important role which it assumes 

 in plants. On the contrary, it is quite certain that, whether visibly 

 diiferentiated into a semi-permeable membrane or merely con- 

 stituted by a liquid film, the surface of the cell is the seat of 

 important forces, capillary and electrical, which play an essential 

 part in the dynamics of the cell. Even in the thickened, largely 

 solidified cellulose wall of the plant-cell, apart from the mechanical 

 resistances which it affords, the osmotic forces developed in con- 

 nection with it are of essential importance. 



But if the cell acts, after this fashion, as a whole, each part 

 interacting of necessity with the rest, the same is certainly true of 



