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- 

 ceUs for the production of the next generation directly 

 from the germ-cells of the parents. 



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



