VEGETATIVE ACTIVITIES OF THE CELL 191 



diffuse. It has been thought wiser, therefore, to confine ourselves, 

 save in one respect, to the latter — the functional activities. 

 Nevertheless, if I have correctly interpreted my duties as in- 

 troducing the subject in order to place in a clear light the con- 

 trolling influence of the nucleus in the life of the cell, I cannot 

 leave these vegetative activities out of account. As opener I 

 must as briefly as is possible, consistent with lucidity, bring 

 forward the evidence of nuclear predominance as afforded by 

 studies upon cell and individual reproduction. It was the 

 studies upon mitosis that first revealed the high importance of 

 this constituent of the cell. 



We can, perhaps, best treat this section of the subject by 

 means of a series of theses : 



1. The properties which distinguish the individuals of any 

 race or family from the individual of any other race or family 

 are to be traced back to the constitution of a single cell, the 

 fertilized ovum, from which that individual has been developed. 



2. There must, therefore, be something in the constitution 

 of the germ matter of the parent stock which differentiates it 

 from the germ matter of other stocks. Nay, more, no two 

 individuals appear to possess germ matter of absolutely identical 

 constitution. 



3. In individuals of gamogenetic origin, resulting from 

 sexual union, the material contributed to the ovum by the 

 paternal spermatozoon and the maternal ovum is, physiologically 

 speaking, of equal value. As demonstrated by Mendel in his 

 observations upon hybrids, like orders of offspring result whether 

 the male cell of stock A be employed to fertilize the ova of 

 stock B, or the female cells of stock A be fertilized bv the male 

 cells of stock B. 1 



It is evident, therefore, that matter of like order is contributed 

 to the fertilized ovum by the two parents. 



4. In studying more narrowly the process of fertilization we 

 find that the only matter contributed correspondingly by both 

 parents is nuclear matter. Ovum and spermatozoon are cells of 

 widely different appearance, and the result of fertilization is 

 that the female cell affords the cytoplasm, or cell substance, of 

 the fertilized ovum ; the male cell provides the centrosome. 



1 In mammals intrauterine existence would seem to introduce a factor of 

 differentiation. 



