PROCEEDINGS OF THE .OHIO ACADEMY OF SCIENCE. 361 



was gradually increased through five selections from 5.6 to 8.6, 

 the mode or most frequent number from 5 to 9. Even more 

 striking is the work of Castle and Phillips on the "hooded" rat, 

 in which two divergent and sharply contrasting types have been 

 separated from an original stock, the extreme of each type lying 

 distinctly beyond any known form of the original stock. It is 

 also very significant to note in this connection that recent, as 

 yet unpublished, work by Jennings and his students shows a 

 much greater degree of variation within pure line cultures of 

 the lower animals, and much greater possibilities for selection 

 within such lines, than the earlier experiments by Jennings 

 himself and by other investigators had indicated. Here again 

 zoological opinion is likely to follow a pendulum course and 

 come to rest in a conservative middle position. 



MENDELISM 



As in the study of variation, so in that of heredity the 

 zoologists must concede that the most conspicuous advance has 

 resulted from the work of a botanist. In 1866 Gregor Mendel 

 published a paper on the hybridization of garden peas, containing 

 the results of eight years' work, in which he had anticipated by 

 a generation the modern method of careful experimentation and 

 accurate statistical record. His essay showed a masterly power 

 of scientific analysis ; but it disappeared from sight in the Pro- 

 ceedings of the Natural History Society of Briinn, and was as 

 if unpublished. The time was not ripe. Lost for a generation, 

 independently rediscovered in 1900 by de Vries, Correns, and 

 Tschermak, translated into English by Bateson in 1902, Mendel's 

 work at once received its deserved but long delayed recognition, 

 thus fairly becoming the property of our quarter century. Since 

 its rediscovery Mendelism has assumed the leading position in 

 all study of heredity and has met with general confirmation; in 

 its widespread extension zoologists have been no less active than 

 botanists. 



A simple breeding experiment, taken from the zoological 

 field, may serve to illustrate the three principles of Mendel's 

 theory. If a pure bred or homozygous black guinea pig is 



