THEORIES OF HEREDITY 



59 



instance, Darwin still held, reproduce the germ-cells. 

 Once the body-cells of the new organism are formed, they 

 are specialized and incapable of assuming the function of 

 germ-cells, simply because, as we shall see presently, they 

 do not any longer contain all the determinants necessary 



FIG. 34. SUMMER EGGS OF MOINA. (After Grobben.) 



(From Weismann, " The Germ-Plasm.") 



A , morula stage ; B, blastula stage ; C, gastrula stage ; g, primitive 

 germ-cells. 



for the upbuilding of an organism. The body, therefore, 

 being incapable of producing the germ-cells anew, there 

 remains the only other possibility of deriving the germ- 

 cells for the production of the next generation directly 

 from the germ-cells of the parents. 



Indeed, in some, though rare, cases such direct relation- 



