246 THE POPULAR SCIENCE MONTHLY 



the nuclear membrane during division. In general the degree of dif- 

 ferentiation may be measured by the degree of unlikeness btween differ- 

 ent cells, and by the completeness with which the protoplasm of different 

 cells is prevented from intermingling. 



All the phenomena of life, including heredity and development, are 

 cellular phenomena in that they include only the activities of cells or 

 of cell aggregates. The cell is the ultimate independent unit of organic 

 structure and function. The only living bond between one generation 

 and the next is found in the sex cells and all inheritance must take place 

 through these cells. Inherited traits are not transmitted from parents 

 to offspring but the germinal factors or causes are transmitted, and 

 under proper conditions of environment these give rise to developed 

 characters. Every oosperm as well as every developed organism differs 

 more or less from every other one and this remarkable condition is 

 brought about by extremely numerous permutations in the distribution 

 of certain parts of the sex cells in maturation and fertilization. Sex 

 is an inherited character dependent upon an alternative distribution of 

 certain chromosomes of the nucleus. There is much evidence that the 

 factors for all sorts of alternative characters are associated with the 

 chromosomes. The differentiation of the oosperm into the developed 

 organism is accomplished in part by the associations and dissociations 

 of germinal units which lead to the formation of new materials and 

 by the segregation and localization of these materials in definite cells. 



Germ cells and probably all other kinds of cells are almost incredibly 

 complex. We know that former students of the cell greatly under- 

 estimated this complexity and there is no reason to suppose that we 

 have fully comprehended it. What Darwin said of the entire organism 

 may now be said of every cell. 



An organic being is a microsome — a little universe, formed of a host of self- 

 propagating organisms, inconceivably minute and numerous as the stars in 

 heaven. 



