EVOLUTION, CYTOLOGY AND MENDEL'S LAWS. 219 



EVOLUTION, CYTOLOGY AND MENDEL'S LAWS. 



By O. F. cook, 



u. s. depabtment of agriculture. 



^T^HE debt of science to theory is a truism. Bad theories are only 

 -L 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 I 



related sciences, embryology and cytolog}\ 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 I 



of each individual organism promised the student of embryology an j 



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 recapit- ' 



ulation could be maintained was perceived by Sir John Lubbock as ' 



early as 1873,* 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, f I 



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 j 



the cell, and thus was opened another highly fertile field of investiga- I 



tion. Instead of mere homogeneous jelly, surprisingly complicated 

 intracellular structures and processes have been discovered and de- 

 scribed, and to identify some of these as the long-sought 'hereditary [ 

 mechanism' is now the dream of the c}'tologist. J 



To judge from his recent article on 'Mendel's Principles of 

 Heredity and the Maturation of the Germ-Cells' + Professor Wilson, 



* * Origin and Metamorphoses of Insects.' "'f^^ "04^ 



t Science, N. S., 16: 506, September 26, 1902. /I" •" ' '■' ' - 



iScience, N. S., 16:991, December 19, 1902. /-'"' C 



;. ■ i 



ft.*' • 



