PRESIDENTIAL ADDRESS. 37 



which is possessed by the nucleus of a germ-cell ; not indeed, 

 as the preformed germs of structure (the gemmules of pangene- 

 sis), but as variations in its molecular constitution ; if this be 

 impossible, such characters could not be inherited " (pp. loo, 



lOl). 



The union of two germ-cells from entirel)^ different indi- 

 viduals always multiplies the number of ancestral germ-plasms 

 by two. The excess is kept down by the removal of the second 

 polar body, as he supposed was proved by its not taking place 

 in parthenogenesis. But the part removed as w^ell as the part 

 retained contains germ-plasms from both parents alike and 

 hence the offspring must partake of the nature of both. 



These ancestral germ-plasms exist in the reprod'uctive cells 

 in vast numbers, and in the removal of half of them at each 

 union of the sexes, there must remain not merely those of the 

 immediate parents, but those of previous generations. If we 

 were theoretically to conceive that at the outset only a single 

 germ-plasm existed from each parent, then the second genera- 

 tion would transmit four, the third eight, and so on in a 

 geometrical ratio, until they would become so numerous as 

 to require the removal of a portion and ultimately always of 

 half the ancestral germ-plasms at each act of reproduction. 

 Says Professor Weismann : " These different qualities are 

 what I have called the ancestral germ-plasms, i. e., the germ- 

 plasms of the different ancestors, which must be contained in 

 vast numbers, but in a very minute quantities, in the nuclear 

 thread. The supposition of a vast number is not only required 

 by the phenomena of heredity but also results from the com- 

 paratively great length of the nuclear thread ; furthermore it 

 implies that each of them is present in very small quantity. 

 The vast number together with the minute quantity of the 

 ancestral germ-plasms permit us to conclude that they are. 



