OF MUTANT CHARACTERS. 



129 



probable that it was derived from a stock different from the line of 

 trident-pattern selection which gave rise to the "with" and to the 

 "without" stocks. The early selection experiments appear to have 

 resulted in four stocks : (1) " without " trident pattern, (2) "without" 

 pure for the original speck, (3) "with " trident pattern, and (4) "olive " 

 stock. The stocks of ' ' with ' ' and of ' ' olive ' ' differed in the character of 

 the trident pattern in that the "with" is a sharp darkening of the trident 

 pattern, while "olive" is a more diffused darkening. Subsequent 

 analysis of the genetic behavior of these stocks showed that the "with" 

 was a simple third-chromosome semi-dominant, while the "olive" was 

 a trimutant stock homozygous for olive II, olive III, which is a third- 

 chromosome recessive mutant not distinguished in appearance from 

 olive II, and "speck," which is a second-chromosome recessive. An old 

 figure (plate 5, fig. 4) bears out our recollection that the original speck 

 was due to a tiny brush of hairs on the side of the thorax above the 

 wing juncture. The new speck is a black pigment spot in the axil of 

 the wing. The original speck seems not to have been dependable in its 

 behavior, while the new speck has behaved with perfect regularity in 

 inheritance. Thus, both the nature of the characters themselves and 

 the nature of the trident mutants associated with the two "specks" lead 

 to the conclusion that they were not the same mutants, as had been too 

 hastily assumed. The new speck from olive stock will be referred to 

 hereafter as speck, while the original speck will be called the old speck. 



DESCRIPTION OF SPECK. 



The character speck, as seen with the magnification with which we 

 ordinarily work (about 15 diameters), is due to the presence of a minute 

 but intensely black round speck in the axil of each wing. The speck 

 is clearly seen from above (fig. 73 a) or from a little below the side 

 (figs. 73 6, 75). Under the microscope the speck is seen to consist of a 



TEXT-FIGURE 73. Speck : a, side view ; fc, from above. 



