1892.] Heredity and the Germ- Cells. 657 
formed, each containing half the chromatin substance of a 
normal nucleus. In the ovary three of these daughter-cells 
abort and the fourth forms a true ovum; in the sperm-gland, 
however, all four daughter-cells form spermatozoa. 
We may thus consider the polar-cell problem as in all prob- 
ability settled; the whole process is probably an inheritance 
or survival of a primitive condition in which all four ova, like 
the four spermatozoa, were fully functional. 
The Relation between the Chromatin and Heredity—We have 
just seen that the last stages in the preparation of the ova and 
spermatozoa for conjugation result in halving the number of 
rods in the original germ-cells. Now, as Hertwig and Weis- 
mann point out, one point is still left in doubt. Why is the 
chromatin substance doubled in the mother-cells so that two 
successive subdivisions are necessary to reduce it to half the 
original quantity? Hertwig has not attempted to answer this 
question, as he prefers to wait for further research. Weismann, 
however, who is unfortunately cut off from research by failing 
eyesight, has offered a speculative solution to this problem 
which he trusts may guide future investigation. 
This leads me to say a few words in regard to his concep- 
tion of the relation of the chromatin to heredity. 1. His first 
premise is that in fertilization there is not a fusion of chroma- 
tin but that a certain independence is preserved between the 
maternal and paternal elements, based upon the observed fact 
that the two pairs of rods do not fuse but lie side by side, and 
upon the assumption that these pairs are kept distinct in each 
cell through all the subsequent stages of embryonic and adult 
development. If this be the case, the hereditary substance 
contributed by the father would remain separate from that 
contributed by the mother, throughout. 2. “Each of these 
pairs would be made up of the collective predispositions which 
are indispensable for the building up of an individual, but 
each possesses an individual character, for they are not entirely 
alike. I have called such units “ancestral plasms,” and I 
conceive that they are contained in numbers in the chromatin 
of the mature germ-cells of living organisms, also that the 
older nuclear rods are made up of a certain number of these. 
