No. 606] 



METHOD OF GENETICIST 



369 



changes are inherited because they result from changes 

 in the chromosomes, and for no other reason; that such 

 changes are usually, if not always, independent of the 

 environment; that such changes produce unpredictable 

 changes in adult structure or function; and that these 

 changes have no reference to the usefulness of the change 

 in the evironment in which the animal exists or in any 

 other environment. 



If one desired to go beyond the first steps of evolution, 

 and discuss the factors that determine the course of evo- 

 lution by etfecting the survival or destruction of such 

 new forms, it would not be difficult to maintain that sur- 

 vival is much less dependent upon fitness than is com- 

 monly supposed, and that natural selection probably 

 operates only to eliminate the most unfit. But such a 

 proposition necessarily involves much speculation, with 

 comparatively little information regarding present day 

 phenomena to serve as guide. I shall content myself, 

 therefore, with the above categorical statement of views 

 regarding the origin of ]iermanent modifications, and 

 allow my colleagues to begin the sifting and testing opera- 

 tion which is theirs to perform. 



LITERATURE CITED. 

 Babcock, E. B., and Lloyd, F. E. 



1917. Somatic Segregation. Journal of Heredity, Vol. 8, No. 2, Feb- 

 ruary, pp. 82-89. 

 Bridges, C. B. 



1913. Non-disjunction of the Sex Chromosomes of Drosophila. Jour- 

 nal of Experimental Zoology, Vol. 15, pp. 587-606. 

 Goldschmidt, R. 



Hyde, R. R. ^' 



1916. Two New Members of a Sex-linked Multiple (Sextuple) AUelo- 



535-580. * 



