304 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



of the two germ-cells is, potentially at least, dual in nature. On the 

 other hand through the process of reduction the gametes are provided 

 with only a single set of such representatives. This duality of the 

 body and singleness of the mature germ is one of the most striking facts 

 that come to light in embryology. How well the facts fit in with the 

 behavior of certain hereditary characters will be seen later in our dis- 

 cussions of Mendelism. 



The cytoplasm not negligible in inheritance. — Just what part is 

 played by the cytoplasm in inheritance is not clear, but it is probably 

 by no means a negligible one. The cytoplasm of a given organism 

 is just as distinctive of the species or of the individual of which it 

 forms a part as are the chromosomes. It is well established that 

 neither nucleus nor cytoplasm can fully function or even exist long 

 without the other, and neither can alone produce the other. They 

 undoubtedly must cooperate in building up the new individual, and 

 the cytoplasm of the new individual is predominantly of maternal 

 origin. It is obvious that all of the more fundamental characters 

 which make up an organism, such, for instance, as make it an animal 

 of a certain order or family, as a human being or a dog or a horse, are 

 common to both parents, and there is no way of measuring how much 

 of this fundamental constitution comes from either parent, since only 

 closely related forms will interbreed. In some forms, moreover, the 

 broader fundamental features of embryogeny are already established 

 before the entrance of the spermatozoon. It is probable th erefore 

 that instead of asserting that the entire quota of ch aracters w hich go 

 " to "make up a complete mdividual are mherited from each parent 

 "equally, we are justified only in m ainiaining~that this"~eq uaTity~ls 

 "restrict ed to those measuraBIe differences which veneer or top off, as 

 it were , the indiv idual. _ We may infer that in the development of the 

 m w being the chromosomes of the egg together with those derived 

 from the male work jointly on or with the other germinal contents 

 which are mostly cytoplasmic materials of maternal origin. 



The chromosomes possibly responsible for the distinctiveness 

 of given characters. -It seems probable that in the establishment of 

 certain basic features of the organism the cooperation of the cytoplasm 

 with chromatin of either maternal or paternal origin might accomplish 

 the same end, but that certain distinctive touches are added or come 

 cumulatively into expression through influences carried, predomi- 

 nantly at least, in the chromatin from one as against the other parent. 

 These last distinctive characters of the plant or animal constitute the 



