248 



THE AMKRICAX XA TCRALIST [ VOL. LI 



tendency among geneticksts to use gene, and its svnouyms factor 

 and determiner, in this sense, which is the second ot the two dis- 

 cussed above. Evidently gene is not properly used in the first 

 sense. A moment s thought, however, will show the impractica- 

 bility of conlmmg factor to that sense; the meaning of this term 

 shifts back and forth continually in common usage, and often 

 remains indefinite. 



Further, when factor (or gene) is used m the second sense, we 

 consider it coextensive with locus (Morgan, 1915. pp. 419-20; 

 Goodspeed and Clausen, 1917, p. 32). A factor is a particular 

 state or condition ot a locus. Let us, then, define locus as the 

 physical unit of segregation, almost certainly identified as a 

 genetically indivisible portion of a chromosome. Genetically in- 

 separable ("completely linked") potentialities, then, belong to 

 the same locus, and hence to the same factor or gene; "completely 

 linked factors" are manily* relegated to non-cytological discus- 

 sion and e^peciiUy to use with the presonc e and-absence ter- 

 minology. 



No doubr ]\remlelian analvsis considers? in any case, only some 

 of tlu' most uadi]> idontifial)lo pioperties of tht real units of 

 segregation concerned, and this tact seems to deserve a large 

 place m our genetic tlunking. Especially is it important that 

 tlie two meanings ot faclor and its synonyms should be clearly 



elianjrcd and (K)imise(l. vagueness and misunderstanding are sure 



* Tlu stud.nl ot -en.ti.s ni l^ uad for eximple (East, 1912), 

 If we f.>r-ct oi rv(l^«. i' d hi ^nn t . ^pv^k wu\ fiictors as particles, 

 onl^ ' M< u t .11 .u. .luul ir I.) tint r mim Ibx \ i.. li Spencer, and 



AVtiMuann No hnu' is ,^Il(d nnd ^^^n f ict- are ob^ urui 



On the otlier hand, he will find the factors of DrosopJnla 

 located with mathematical exactness m diagrams of the chromo- 

 .somes, and often apparently or explicitly considered as material 

 components of the eliromosomes. In the interest ot clear think- 

 ing, espcclallv in tlie f'a>>> of bcLMniKTs and cnsual .students in the 

 fipld or L't'iiclicN- tlic (>xpl;iri;i; 1(111 o| this a!)parent contradiction 



As an example ot the wav in which this terminological con- 

 flict mav cloud an armmient when the essential facts are clear to 

 the writer we mav take the following case. iVIorgan (1913, 



