Factors not alternates may or may not
separate--the distribution is largely a matter of chance.
Such are the fundamental principles of Mendelism; but on them was early
grafted a theoretical structure due mainly to the German zooelogist,
August Weismann. To understand his part in the story, we must advert to
that much mooted and too often misunderstood problem furnished by the
chromosomes. (See Fig. 46.) These little rods of easily stained
material, which are found in every cell of the body, were picked out by
Professor Weismann as the probable carriers of heredity. With remarkable
acuteness, he predicted their behavior at cell-division, the intricate
nature of which is usually the despair of every beginner in biology.
When Mendelian breeding, in the early years of this century, showed
temporary pairing and subsequent separation of units in the
germ-cell, it was soon realized that the observed facts of breeding
fitted to a nicety the observed facts (predicted by Weismann) of
chromosome-behavior; for at each cell-division the chromosomes, too,
pair and separate again. The observed behavior of transmitted characters
in animals and plants followed, in so many cases, the observed behavior
of the chromosomes, that many students found it almost impossible to
believe that there was no connection between the two, and Dr.
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