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 codperate 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 spermatozoén. It is probable therefore 
that instead of asserting that the entire quota of characters which go 
to make up a complete individual are inherited from each parent 
equally, we aré justified only in maintaining that this equality is 
restricted to those measurable differences which veneer or top off, as 
it were, the individual. We may infer that in the development of the 
new 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 codperation 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 
