| EVOLUTION, CYTOLOGY AND MENDEL'S LAWS. |
By O. F. COOK,
U. S. DEPARTMENT OF AGRICULTURE.
THE debt of science to theory is a truism. Bad theories are only less valuable than good ones, and for some purposes they are even better. We do not arrive where we expected to go, but reach; an undiscovered country which a more direct route would have left unexplored. The recent history of biology furnishes two excellent examples of the fertility of false theories in the development of the related sciences, embryology and cytology The theory of organic recapitulation, to the effect that the phylogeny or evolutionary history of natural groups must be repeated in the ontogeny or development of each individual organism promised the student of embryology an easy wealth of scientific discovery, and within a few years hundreds of razors were paring thin the mysteries of evolution. Libraries of new facts were discovered and published, but as our knowledge of life histories increased there was a corresponding decline in the probability that any particular stage in the growth of the individual is necessarily more ancestral than any other. That no general doctrine of recapitulation could be maintained was perceived by Sir John Lubbock as early as 1873,[1] but vertebrate embryologists did not permit their zeal to be dampened by even the most obvious facts of entomology. Indeed, one of our prominent investigators, finding that recapitulation is elusive by microscopical methods, now proposes to test it by breeding experiments, the results of which may be available in a future geologic epoch.[2]
The organism having been followed back to its unicellular stage without discovering any process or mechanism by which its adult form was predetermined, believers in such a device must needs seek it inside the cell, and thus was opened another highly fertile field of investigation. Instead of mere homogeneous jelly, surprisingly complicated intracellular structures and processes have been discovered and described, and to identify some of these as the long-sought 'hereditary mechanism' is now the dream of the cytologist.
To judge from his recent article on 'Mendel's Principles of Heredity and the Maturation of the Germ-Cells'[3] Professor Wilson,
