HISTORY OF THE FERTILIZATION PROBLEM 17 



germinal vesicle by karyokinetic divisions. Thus the 

 genetic continuity of the germ nuclei with nuclei of 

 preceding cell generations was established. As yet the 

 character of the fusion of egg and sperm nuclei had 

 hardly been raised, for the chromosome problems and 

 hypotheses were in a nascent state. Flemming's dis- 

 coveries concerning chromosomes and their reproduction 

 in karyokinesis by splitting date only from 1876-78. 



All the problems of cell morphology were in a fine 

 state of fermentation during this time, the really classic 

 period of cell morphology; the foundations of our present 

 knowledge of cell division were being laid; before the 

 decade 1870-80 it had been firmly established that cells 

 arise only by division from pre-existing cells; but two 

 views of the origin of nuclei were still held, one that of 

 free formation, according to which the nuclei of daughter- 

 cells had no genetic connection with the nucleus of the 

 mother-cell, and the other that nuclei arise by division 

 from a preceding nucleus. Little by little as a result 

 of numerous investigations by many investigators, both 

 zoologists and botanists, the matter cleared up. In 

 1878 Flemming was able to outline the whole scheme 

 of karyokinesis substantially as we now understand it. 



The fundamental biological principle of genetic con- 

 tinuity was foreshadowed by the founders of the cell 

 doctrine and was more or less distinctly foreseen by some 

 of their contemporaries, as in the case of Lallemand. 

 It was yet more clearly expressed in Virchow's famous 

 aphorism, omnis cellula e cellula (1856) ; but it could not 

 become an established guiding principle in genetic 

 research until the entire cell cycle of the individual life- 

 history was worked out in broad outline, until the process 



