In Pursuit of the Gene

CELL BIOLOGY © 147
make clear the crucial fact that new cells were created by the process of binary
fission. 4
The next great leap forward in the cellular study of heredity was taken
by Virchow’s student Ernst Haeckel, who would become a leading disseminator
of the theory of evolution, perhaps more influential than Darwin
himself, as well as a great believer in the importance of German racial
purity. 5 Drawing on the knowledge he had gained as Virchow’s student, in
1866 Haeckel made the astonishingly perceptive speculation that it was the
cell nucleus that controlled heredity. Without providing a shred of evidence,
he boldly declared: “The inner nucleus is responsible for the transmission
of the inheritable characteristics, while the outer ‘plasma’ is responsible
for the accommodation of or adaptation to the conditions of the
environment.” 6
Haeckel’s insight was all the more remarkable in light of the fact that
biologists of the time believed that the protoplasm was responsible for all
the basic functions of life, including those of heredity. Furthermore, there
was little to support the idea that the nucleus played the role Haeckel assigned
it and much to recommend against it, the main problem being that
the nucleus seemed to disappear at the beginning of the cell division process,
dissolving into the cytoplasmic soup without a trace.
In 1874 Leopold Auerbach, who had studied histology, embryology, and
microscopy with Robert Remak at the University of Berlin, produced a series
of striking drawings of the large, clear germ cells of a threadworm of
horses (Ascaris), which gained worldwide recognition. 7 With remarkable
clarity and detail, Auerbach’s drawings depicted the fusing of two nuclei in
the formation of the fertilized egg and the subsequent cell division.
Although Auerbach had carefully observed the fusing of the two nuclei
in the fertilized egg, he missed the crucial fact that the two nuclei were
the sperm and egg nuclei. 8 But Auerbach’s paper was soon read by Oscar
Hertwig, who together with his brother Richard was part of Haeckel’s circle
in Jena. Immediately after reading the paper, Hertwig dropped everything
to study fertilization in the sea urchin, whose large translucent egg cells
were ideally suited to the purpose. 9 Five to ten minutes after spermatozoa
were added to a suspension of ripening eggs, Hertwig observed, a second