No. 631] NOTES AND LITE B A TV RE 



191 



tion theory as held at that time was untenable when applied 

 either to the origin of species or to the origin of diameters. 

 What has since happened is that the mutation theory has been 

 frankly abandoned as applied to such origins and is now limited 

 to the origin of factors or genes. It is recognized that charac- 

 ters may change progressively and permanently (just as Whit- 

 man believed they did) under the guidance of selection. The 

 agency of such change is now supposed to he modifying or mul- 

 tiple factors, so nunierou 1 1 t t 1 ftl letection and 

 so frequently coming and going that gradual modification of 

 characters in a desired direction is not difficult. This is the re- 

 siduum of truth which underlay the mutation theory as Whit- 

 man knew it and attacked it. In this marvellously modified form, 

 he would probably not have attacked the theory at all. 



Volume 2 deals chiefly with inheritance, sex, and color in hy- 

 brids of wild species of pigeons. An enormous amount of exper- 

 imental data is here recorded, and scattered notes, briefs for 

 lectures, etc.. have been brought together by the editor, dealing 



superiority as genetic material of the pure species with which he 

 worked, since he was unable to produce in any ease a second gen- 

 eration of hybrid birds, had no adequate basis for discussing 

 heredity in his hybrids, and no adequate basis for criticizing 

 Mendel ism which is revealed only in the F, generation. One 

 characteristic of the large number of sterile F t hybrid birds 

 whir!. Whitman produced is noteworthy. Their characters were 



significance of blending is, whether it is essentially different in 

 nature from Mendelian inheritance, Whitman thought rightly 



