662 The American Naturalist. [August, 
the potential of the nucleus is differently exerted. Here, again, 
we have the idea of patent and latent hereditary elements, 
‘such as appear in the entire individual upon a larger scale. 
This is one of the most interesting problems for future inves- 
tigation, but the direction of research will, I imagine, cover a 
larger area of cell-content than the nucleus, as we are now 
swinging back to regard the extra nuclear archoplasm as an 
important factor in the process. 
In the following paragraph Hertwig expressed his view of 
nuclear control and cytoplasmic differentiation : ; 
“ As I saw in the transformation of the nucleus during fer- 
tilization proof that it is the bearer of hereditary substance I 
recognized a great advance in the fact that the nucleus leaves 
in the same form in every cell, and in its vesicular capsule is 
somewhat removed from the metamorphoses of the cells. As 
Nägeli spread his idioplasm as a net-work throughout the 
whole body, so, according to my theory, every body-cell con- 
tained in its nucleus its quota of hereditary substance, while 
its specific histological peculiarities were to be regarded as its 
plasma-products.” 
2d. The next question is the fate of the maternal and pater- 
nal contributions to the embryo. Here there is a wide difference 
of opinion. On the one side Van Beneden is the leader of 
those who regard each cell of the body as in a sense hermaph- 
rodite; as we have seen, his views of maturation and the sig- 
nificance of the extension of the polar bodies were colored by 
this theory, for he regarded the germ-cells as hermaphrodite 
until one sex was eliminated. But now that the researches of 
Hertwig have given the last blow to Van Beneden’s theory, 
and it follows that there can be no male and female chroma- 
somes, there still remains room for the analogous view that the 
maternal and paternal chromasomes remain distinct through- 
out the course of development, not as sexual elements but as 
substances with the same racial and specific but different indi- 
vidual tendencies. Rabl, an eminent embryologist, shares this 
view, and it is supported by Boveri upon the observation that 
in each division the paternal and maternal elements are kept — 
distinct, and in Ascaris, for example, two of the chromasomes — 
