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ZOOLOGY: E. a CONKLIN 
male and not by the male germ cells in plants (Baur, Shull) ; the trans- 
mission in the egg cytoplasm of fat stains, chemical substances, im- 
munizing bodies and possibly parasites prove that, "at the time of 
fertilization the hereditary potencies of the two germ cells are not equal, 
all the early development, including the polarity, symmetry, type of 
cleavage, and the relative positions and proportions of future organs 
being predetermined in the cytoplasm of the egg cell, while only the 
differentiations of later development are influenced by the sperm. In 
short, the egg cytoplasm fixes the type of development and the sperm 
and egg nuclei supply only the details" (Conklin 1908). 
Ontogeny begins with the differentiation of the egg in the ovary and 
not at the moment of fertilization; at the latter time some of the most 
general and fundamental differentiations have already occurred. In- 
deed the cytoplasm of the egg is the more or less differentiated body 
of the embryo. 
3. Is Inheritance through the Egg Cytoplasm Non-Mendelian? — ^When- 
ever a character is transmitted as such through the egg cytoplasm and 
not as factors in the chromosomes of egg and sperm it is not inherited 
in Mendelian fashion. Thus if chromatophores are transmitted from 
generation to generation in the cytoplasm of the egg and are at no time 
influenced by the sperm, their mode of inheritance is non-Mendelian. 
If the polarity, symmetry and pattern of the egg do not arise during 
oogenesis, but are carried over unchanged from generation to generation 
they are also non-Mendelian characters. With regard to the polarity 
of the egg, it is not certain whether it is transmitted in this manner or 
not; but its symmetry and pattern of organization are evidently developed 
anew in each generation. It is a significant fact that in oogonia and 
spermatogonia the volume of the nucleus is sometimes greater than 
that of the cytoplasm, and in all cases it is relatively greater in early 
stages of the genesis of the sex cells than in later ones. In general the 
relative volume of nucleus and cytoplasm is a good measure of the 
differentiation of the latter. Most of the cytoplasmic differentiations 
of the egg and sperm arise during the genesis of those cells, just as in 
the case of tissue cells. Nerve cells and muscle cells differentiate under 
the influence of maternal and paternal chromosomes, and undoubtedly 
the same is true of most of the differentiations of egg and sperm; but 
while some of these egg differentiations persist in the new individual 
those of the sperm do not. Consequently, in each generation the egg 
contributes more than the sperm to ontogeny. There is cytoplasmic 
inheritance through the female only, but these cytoplasmic characters 
.are themselves of biparental origin. 
