14 CELL ORGANS [CH. 



of protoplasm to a neighbouring nucleated mass, and some 

 were without nuclei and quite separate. The nucleated 

 masses, and also those with no nucleus which were connected 

 by a strand to a nucleated mass, both after a time secreted 

 new cell-walls around themselves, but the non-nucleate 

 masses produced no cell-wall and gradually died. Another 

 interesting observation showing the influence of the nucleus 

 on the cell-protoplasm was made by SCHAUDINN. He found 

 that in the Foraminifera, when the pseudopodia of two 

 individuals of the same species came into contact they fused 

 and united with one another if the nuclei of the two animals 

 were in the same condition, but when one individual was 

 multinucleate and the other in the condition of having only 

 one nucleus, or if one was undergoing nuclear division and 

 the other in the resting stage, then no fusion of the pseudo- 

 podia took place. Observations of this kind indicate that 

 the nucleus in some way controls the metabolic activities of 

 the cell, and it probably also plays an important part in 

 determining the various modifications undergone by the 

 cells of the different kinds of tissues, though it perhaps has 

 not the exclusive role in this respect which has sometimes 

 been ascribed to it. Some account of the evidence with 

 regard to the function of the nucleus in the transmission of 

 hereditary characters will be given in a later chapter. 



Before passing on to consider the structure of the nucleus, 

 it may be appropriate to mention a theory which has played 

 a considerable part in cytological investigations the theory 

 of R. HERTWIG that in any species the volume of the nucleus 

 bears a fixed ratio to the volume of the cytoplasm dependent 

 on it. This theory, known as that of the " karyo-plasmatic 

 ratio," or often by its German name of "Kernplasma- 

 relation," originated from the study of the Protozoa, but 

 has received considerable support from observations on 



