40 THE MAIN CURRENTS OF ZOOLOGY 



elements are formed in these hybrid plants two 

 classes of germ-cells will arise in equal number, one 

 class carrying the dominant and the other the reces- 

 sive quality. Chance combinations of these germ- 

 cells will yield on the average, one union of dominant 

 with dominant, one union of recessive with recessive, 

 and two combinations in which dominant and reces- 

 sive are united. In the latter instance the dominant 

 will be the visible character, the recessive, though 

 present, being invisible. This segregation of the 

 gametes into two sets of "pure" gametes was recog- 

 nized by Mendel in an attempted theoretical explana- 

 tion of his observed facts, and, in view of the state of 

 knowledge at the time, showed remarkable analytical 

 ability. 



Mendel's papers were published in 1866 and 1867 in 

 the proceedings of the Natural History Society of 

 Briinn, but their importance was overlooked for 

 nearly thirty-five years. The periodical in which 

 they appeared was not widely known, and moreover, 

 the minds of naturalists at that time were largely 

 occupied with the questions of organic evolution 

 raised through the publications of Darwin. In the 

 year 1900, however, the great principle of heredity 

 worked out by Mendel was independently redis- 



