34 BIOLOGICAL LECTURES. 



the cells which are formed by division ; it is determined rather 

 by the general cytoplasm. In the later stages of karyokinesis, 

 after the lobing of the cytoplasm has indicated the size of the 

 daughter cells, but sometime before the division-wall is formed, 

 the asters become unequal in size if the division is to be an 

 unequal one, and by the time that the division-wall is formed 

 the asters are proportional in size to the daughter cells in 

 which they lie. At a considerably later period the nuclei 

 become proportional in size to the cells in which they are 

 found. 



In Crepidula, therefore, I believe it is certain that the direc- 

 tion of the cleavage, as also the position, the shape and the 

 size of the resulting cells are not directly governed by the 

 nucleus. These definite forms of cleavage which are so 

 excellently exemplified in Crepidula are inherited as certainly 

 as any definite adult structures are, and if they are not 

 under nuclear control, these hereditary tendencies must be 

 transmitted through the cytoplasm. 



Of course, it may be urged that there is some unknown and 

 invisible influence emanating from the nucleus which controls 

 all the processes of cell life. In the nature of the case such 

 an assertion cannot be affirmed nor denied on the ground of 

 observation, and it seems to me sufficient to urge in reply that 

 we should believe things are what they seem unless we are 

 compelled to believe differently. Many of the processes of 

 cell life seem to be controlled by the cytoplasm more inti- 

 mately than by the nucleus ; so far as we can observe, all 

 cytoplasm comes from pre-existing cytoplasm, just as all 

 nuclei come from previous nuclei. We know that the cyto- 

 plasm from both the father and mother are represented in 

 every stage of fertilization, and it is unnecessary and therefore 

 unscientific to assume that the nucleus controls all the 

 processes of cell life, and that the heritable characters of the 

 cytoplasm are transmitted only through the nucleus. 



If, in stating my objections to the view held by the vast 

 majority of the biologists of the present day, I may seem to 

 have denied the importance of the nucleus while emphasizing 

 the importance of the cytoplasm, I would wish to say, in con- 



