No. (iO.)] snoh'TKU AHTICLKS AND DISCUSSION 



303 



for reduced color, mid tlu'>c six .hlulcrs winch bv themselves produce 



stae-e from the dark v.Hnwisli pink ,>r tlie oosin female to pure white 

 (Bridsres. 1916. p. 1 111). 



Thus we see tliat in l)ri>si>i>h wr i-ould -jvt t in' samr M)i-t of 

 graded results tli;il Cjisii,' dors with liis r;its. m l>n>si>i>lnlu 



coutroversy is as to the occurrence oL niiinUr rlianuvs m ilir 

 liereditarv constitution, and their ficcuimilation l)v s,'icct ion : so 

 that by selection various grades of a <iiv('ii oxtt'nial idiarartor 

 can be obtained. In Drosophiln. according to lind^ts. su.ii 

 changes occur; changes which give, so far as our ])irs(Mit impoi- 

 feet knowledge goes, at least seven diver.se grades ut a smnlo 

 tint (that IS itself, as we shall note, only one gfa.lo in anothor 

 serus t NM. In un glides) B> mems < t th nil 

 chin^vs uno .-niild nl.tiiin. by the mutationist s u n 1 ii ni nt 

 the continiioiish m-adod vi.sible results which mI Hon at-tuallv 

 gives, is not tlieii the controversy as to the etTectivciiess ot stdec- 



As to just where the graded hereditary changes occur there 

 remain indeed certain differences of opinion: some selectionists, 

 like Castle, hold that the various grade-s ot a given external char- 

 acter are due to diverse minute modifications of the same unit 

 character — of the same locus in the chromosome; while, as we 

 have seen, the modifying factors are due to changes in diverse 



