VOL. XLIX, NO. 581 



MAY, 1915 



THE 



AMERICAN 

 NATURALIST 



A MONTHLY JOURNAL 

 Devoted to the Advancement of the Biological Science! with 



Special Reference to the Factors of Evolution 



I- On the Nature of the Conditions which determine or prevent the Entrance 



of the Spermatozoon into the Egg. Jacques Lokb - 

 U. Germ Cells and Somatic Cells. Leo Loeb ------- 



in. Mendelian Inheritance of Fecundity in the Domestic Fowl, and Average 

 Flock Production. Dr. Raymond Pearl ------ 



IV. Shorter Articles and Discussion : The Appearance of Known Mutations in 

 Other Mutant Stocks : Professor T. fl. Morgan and Harold Plough. 

 The Evening Primrose Varieties of De Vries : John Belling - - 



THE SCIENCE PRESS 

 .STER, PA. GARRISON, ft. f . 



NEW YORK: SUB-STATION 8* 



