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of the parent has undergone variation, this will be represented in the egg 

 by the gemmules of the part and may thereby be inherited. The im- 

 mense number of gemmules required to effect the results, as well as the 

 lack of sutticient evidence of a positive kind in favor of Darwin's theory, 

 have prevented its general acceptance. 



On Weismann's theory, heredity follows from the assumption that both 

 parent and offspring are derived from the same mass of germ plasm. 

 That which had given origin to the parent must be expected to develop 

 into a similar organism in the offspring. That the germ-plasm develops 

 into the peculiar structure and form of both is due to its molecular struc- 

 ture, the result of gradual modifications which have been accumulating 

 during the ages that have elapsed since their earliest ancestor received 

 its being. 



Some extremely important conclusions issue from the acceptance of 

 this theory of AVeismann's. If the germ-plasm, borne about in the body 

 of any organism, protected and nourished by it, does not have its mole- 

 cular constitution, on which the character of the offspring depends, at 

 all affected by the state of the parent's body then none of what are called 

 acquired characters can be transmitted from one generation to another. 

 This fact, if fact it be, strikes at the very root of other promising theo- 

 ries. Then none of the results of the use and disuse of organs will be 

 transmitted; none of the direct effects of the climate or soil, or any of the 

 environment on the body of the parent, will show in the descendants ; 

 nor will any mutilations be inherited. The heat or the cold, the drought 

 or the Hood, may produce the most profound effects on the animal or the 

 plant, in the way of altering its form or structure or color, but the off- 

 spring will not directly inherit any of these results. 



Since, however, Weismann firmly believes that existing species have 

 been derived from older species by descent and modification, how does 

 he account for the variations that must have arisen ? This is done on the 

 theory of sexual mixture. The germ-plasm of every individual of every 

 species has certain peculiarities, which are passed on, with greater or less 

 intensity, to the next generation. The male animal or plant has certain 

 hereditary tendencies, that of the female different tendencies. When the 

 germ-cells of the two individuals have united, an organism develops that 

 is different in some respects from both the parents, being, as Weismann 

 expresses it, a compromise between the two developmental tendencies. 

 Since the numbers of individuals of every species are numerous and no 



