Modification of Germinal Constitution of Organisms 143 



subsequent hypotheses of the peripheral origin of modifi- 

 cations and of their inheritance. 



The hypothesis of the peripheral origin and transmission 

 of variations is shown in diagram in Fig. 57-4, where the 

 cause of variation (x) impinges upon the organism and 



External cause of somatic 

 modification 



PARENTS 



PROGENY 



FIG. 57. (A), Diagram to represent Darwin's Provisional Hypothesis of 

 Pangenesis and current neo-Lamarckian conceptions and (B), the continuity of 

 the Germ Plasm Hypothesis of Weismann. 



induces a change, variation (y), and from the cells composing 

 this modified part, as from all other cells of the body, 

 gemmules, minute masses of matter, electrolites, or some- 

 thing, are thrown off and these units conserve the power of 

 reproducing the replica of the part from which they come, 

 either normal or modified. These gemmules are supposed to 

 be gathered in the gametes, and in reproduction are supposed 



