544 



ITURAL1ST [Vol. LII 



long epochs of time, as well as from the evidence of the 

 non-contamination of genes (hiring diverse environments. 



II. The mutations demonstrated by DeVries and oth- 

 ers, together with the variations obtained by Castle, are 

 to be interpreted as a result of the combinations of exist- 

 ing genes. The mutations noted by Morgan and his as- 

 sociates, as evidenced from recurrence and stability, are 

 in the nature of modal fluctuations having no definite 

 cumulative value. 



III. The direction of axial rotation in aquatic micro- 

 organisms is best explainable on the basis of the appar- 

 ent east-west motion of the sun having influenced the 

 movement of the organs of locomotion. Thus the charac- 

 ter becomes one acquired from external stimuli, and the 

 persistence of reverse forms in both the northern and 

 southern hemispheres indicates the hereditary nature of 

 tie- character. Morphological characters, such as the 

 stria 1 , etc., may arise in a similar manner or through se- 

 lection. By correlation with the preceding characters, a 

 cumulative and irreversible effect is produced. 



IV. The primary factors in evolution are environ- 

 mental and thus dynamic. The secondary factors of a 

 combinational nature are gradually approaching a limit- 

 ing maximum value, and are thus becoming static. 



BIBLIOGRAPHY 



1917. Piebald Bats and Multiple Factors. Am. Nat., pp. 102-114. 

 1917. Bole of Selection in Evolution. Jouni. Wash. Acad. Sci., Vol. 

 6, pp. 369-387. 



