1*4 THEORIES OF HEREDITY AND VARIATION. 



kinds of cells are known as male cells (spermatozoa) and female 

 cells (ova), and may be borne by different individual as in most 

 animals, or by the same individual as in the flowers of most plants. 

 When there is a union or coalescence between an ovum and a 

 spermatozoon the resulting cell has the power, under proper con- 

 ditions, of developing into a complete individual of the parent 

 species. 



Weismann's theory is that, in the formation of a new individual 

 out of this compound cell, all of the germ plasm which constitutes 

 it is not used up in the production or growth of the individual, but 

 that part of it is carried over intact within the body of the new 

 individual, and is the material which originates the growth of more 

 germ plasm in the later life of this individual. In other words, he 

 holds that the germ cells grow only from germ cells, and not at all 

 from somatic cells. As we know that somatic cells are the differ- 

 entiated descendants of germ cells, and have no conclusive evidence 

 that germ cells are produced from somatic cells, there is much 

 reason in Weismann's contention. In fact, the very definition of 

 germ cells and somatic cells implies that the first are for reproduc- 

 tion and the second are not. The relationship of germ cells to 

 somatic cells is like the relationship of bees in a hive to each other, 

 where the queen is for reproduction and the workers are incapable 

 of reproduction, but act simply as gatherers of material to support 

 the colony. 



THE ISOLATION OF GERM CELLS. 



While the germ cells are housed within and are nourished by 

 the body (the soma), the followers of Weismann insist that that 

 fact does not at all affect the germ cells as such, because they are 

 completely removed from external conditions and their surroundings 

 are so nearly identical, under all circumstances and through any 



