238 T. H. MORGAN. 



failed, because, as we now think, these are only juvenile char- 

 acters. The dot is sometimes seen in young spot flies, but is weak 

 and soon disappears. Dot and dash are, therefore, due to the 

 same mutation that gave the spot, but are ephemeral and are 

 especially seen in the double recessive condition black spot. 

 The different degrees of viability shown by the different muta- 

 tions may also be looked upon as effects associated with the 

 mutation effects of the highest importance in determining the 

 chances of survival of the mutants, but of small value as indi- 

 cators of the mutation itself. 



LINKAGE OF SPOT AND WHITE. 



If, as the evidence shows, spot is an allelomorph of yellow,, 

 and both have a common normal allelomorph, it was not con- 

 sidered worth while to carry out any extensive experiments in 

 linkage, since the data for yellow would apply to spot. Inci- 

 dentally, however, a few experiments were made with white-eyed 

 flies, and may be given here. 



A few yellow white males were bred to spot red-eyed females. 

 The FI flies were yellow red females and spot red males. These 

 inbred gave: 



Yellow Red 9. Spot Red 9 . Yel. White cf- SpotRedc?. Yel. RedcT. Spot White cf. 



(1) 63 IQ 40 31 O I 



(2) 94 21 47 60 i o 



The linkage of spot and white shown by these figures is i.n. 

 That already determined for yellow white is 1.12. The coinci- 

 dence is greater than might be expected with small numbers for 

 loci so near together. 



In another experiment a spot black, red-eyed male was mated 

 to a yellow white-eyed female. The daughters were yellow red,, 

 the sons yellow white flies. These inbred gave: 



Females. 



Yellow Red. Yellow Black Red. Yellow White. Yellow Black White. 



45 ii 4i 9 



Males. 

 Spot Red. Spot-black Red. Yellow White. Yellow-black White.. 



39 13 33 12 



The analysis follows: 



