No. 609] 



THE THEORY OF. THE GENE 



523 



set of allelomorphs has the same locus in the same chromo- 

 some) this experimental evidence shows that several 

 allelomorphs of the same gene may exist. An interesting 

 relation In regard to these nmltiple allelomorphs is that 

 they affect chiefly tlie same part of the body in the 

 same general way. They maij give a series of types that 

 is discontinuous, such as the (|uadru]>le mouse series: 

 yellow, gray w^iite-belly, gray, black; or the more nearly 

 contiimous sei)tu])le DrosopliHa series: red, blood, cherry, 

 eosin, buff, tinged, white. AVhether such a series of 

 cliaracters is large enough to appear continuous or not is 

 a matter of trivial importance in comparison with the es- 

 tablished fact tiiat the genes behind such a series arose in 

 the same way as do other nmtant genes, and after they 

 have ap])cared, are as constant as are other genes. There 

 is no cxpciiuicnt.-il evidence to show^ that the multiple 

 ninl.'iiir aM('h)ni()i-i)lis are more likely to arise from each 

 other Ihnii they .-ire from the normal allelomorph, and 

 even if this slionid he time for individual genes it is no 



w^hich nmtate moi-e rt'adlly thiui others. iMnerson has 

 shown for corn that one allelomori>li of a series is more 

 likely to nmtate than others and we have shown for 

 Drosophihi that certain normal genes, as the one that 

 unit-Mr^ to pnulu.-e v,M-mi'i..n e color, are more likely 

 to nmtate than are others. 



WImmi .leiminu-' rri(^s to interpi-et this evidence of con- 

 timn)ns <erie- ot' allelomoi-phic chai'acters as breaking 

 down all real distinctioii between nmtation and continuous 

 variation, lu' leav- out of account certain very funda- 

 mental consi(h.ra.ti(Uis. For example. De Vries himself 

 has always ui'ged that mutati(ms may he very small so 

 far as the character .•hanuv is concerned: tln^ Svjdiif evi- 

 dence show- rhi- in a vcr> Mrlking way, and Johann- 

 sen'> bean- Ma\-e been t'or si"\-eral years a classic case 

 illu.-tratuiu- how tniiiute the characters depending on 



