226 PHYSICAL BASIS OF HEEEDITY 



zoon to develop into an embryo, while we can induce the egg to develop 

 into an embryo without a spermatozoon. This may mean that the 

 protoplasm of the egg is the future embryo, while the chromosomes of 

 both egg and sperm nuclei furnish only the individual characters. 



The evidence from Mendelian heredity is adverse to 

 any such distinctions as those made by the three authors 

 referred to above. We find in them, I think, an echo of an 

 old and somewhat mystical conception of fundamental dis- 

 tinctions between order, family and generic characters 

 of animals and plants — ^distinctions that even most syste- 

 matic writers recognize to-day as little more than conven- 

 tions that change from group to group. In the second 

 place, since the cytoplasm of the egg has been under the 

 influence of its own nucleus with a paternal and a maternal 

 group of chromosomes there is no direct means of deter- 

 mining whether its characteristics are due to such an 

 influence or have always been free from it. The fact that 

 sperm of a foreign species does not change the cytoplasm 

 of the egg at once is to be expected even from a chemical 

 viewpoint. Mendelian workers can find no distinction 

 in heredity between characteristics that might be called 

 ordinal or specific, or fundamental, and those called 'indi- 

 vidual.'' This failure can scarcely be attributable to a 

 desire to magnify the importance of Mendelian heredity, 

 but rather to experience with hereditary characters. That 

 there may be substances in the cytoplasm that propagate 

 themselves there and that are outside the influence of the 

 nucleus, must, of course, be at once conceded as possible 

 despite the fact that, aside from certain plastids, all the 

 Mendelian evidence fails to show that there are such char- 

 acters. In a word, the distinction set up between generic 

 versus specific characters or even ''specificity'' seems at 

 present to lack any support in fact. 



