220 COOK 



prove conclusively that the recessive character may not be lost 

 or diminished by this period of suppression, but may have 

 equal representation in the expression-tendencies of the gametes 

 of the next generation. 



Single gametes, like conjugate gametes, may retain and 

 transmit characteristics which they do not express. The reap- 

 pearance of the blue plumage of the wild pigeons in Darwin's 

 crosses of white varieties, the return of the red and yellow 

 feathers of the wild jungle-fowl to Professor Davenport's black 

 and white chickens, and the uniform production of black-eyed 

 mice as a result of crossing two pink-eyed varieties by Darbi- 

 shire, are conspicuous examples of this fact, that characters 

 may be brought again to expression after passing in latent con- 

 dition through many generations of germ-cells. 



With this fact definitely established, that it is possible for 

 germ-cells to transmit characters for many generations without 

 bringing or tending to bring them into expression, the Mendelian 

 " laws of disjunction," *' purity of gametes," " alternative inher- 

 itance," or whatever they may be called, become at once super- 

 fluous and inadequihe. They are inadequate because they do 

 not explain how a character-unit could once get back into 

 gametes after being left out. They are superfluous because the 

 facts indicate only that gametes have a tendency or polarity of 

 expression of particular characters, though they may at the 

 same time transmit other characters which can regain the power 

 of expression in subsequent generations. 



MENDELIAN INHERITANCE OF MUTATIONS. 



Belief in the Mendelian assumptions of character-units and 

 pure germ-cells as general laws or principles of descent has 

 been greatly strengthened by contemporaneous activity in the 

 investigation of the phenomena of mutative variation. Mutative 

 variations commonly obey Mendel's "laws." It is not strange 

 that those who have accepted mutations as genuine species 

 should consider the Mendelian "principles of inheritance" as 

 of universal application, and of fundamental significance for 

 evolution. 



That there are very direct relations between mutations and 



