OF MUTANT CHARACTERS. 245 



distribution of the pigment is very definite, however. The scut^^lhim 

 is largely or entirely dark and the base of the trident pattern on the 

 thorax is broader and much heavier, while the prongs are scarcely 

 darkened at all. The characteristic feature of trefoil is tlie presence 

 of extra basal sections to the trident outside the regular region. These 

 side areas are fully as dark as the central parts and extend forward 

 even farther. Another region that is dark in trefoil but not in the 

 other thorax patterns is a patch behind each eye on the back of the 

 head. These eye-patches and the side-prongs are the niiiin characters 

 used in classifying trefoil. 



INHERITANCE OF TREFOIL. 



In out-crosses to wild, trefoil behaved as an autosomal recessive, 

 giving only wild-type flies in Fi, and reappearing as about a quarter 

 of the F2 flies. 



CHROMOSOME CARRYING TREFOIL. 



F2 from the cross of trefoil to pink gave a 9 : 3 : 3 : 1 ratio, while 

 the corresponding cross to curved gave a 2 : 1 : 1 : ratio, from which 

 it was seen that the locus of trefoil is in the second chromosome. 



LOCUS OF TREFOIL. 



It was found that trefoil and black together gave a very dark fly 

 which was distinguishable from black. With some difficulty a triple- 

 recessive black strap trefoil stock was made up to test the locus of tre- 

 foil. This stock was never used, but from the indications met with in 

 its synthesis it seemed probable that the locus of trefoil is not far from 

 that of black, but between black and strap. This was confirmed 

 roughly by a star trefoil back-cross which gave 42.1 per cent of crossing- 

 over (S 34, tf 55, S tf 42, -f23). The locus is thus at about 50.0 

 with reference to star. 



VALUATION OF TREFOIL. 



Considerable difficulty was met with in the classification of trefoil 

 from the variability of the character, and for this reason there was no 

 strong incentive to establish its locus or to use it in any way. 



CREAM b (cj. 



(Plate 5, fig. 11.) 



ORIGIN OF CREAM b. 



An eosin female from a stock of non-disjunction, when mated to a 

 bar male, gave (culture 82, March 10, 1914) among the eosin sons one 

 whose eye-color was as light as tliat of cream II or cream III. This 

 male was out-crossed to a wild female and in Fo gave creams among 

 the eosin sons but no disturbance of the color of the not -eosin flies 

 (cultures 183, 184, 185). The F2 ratio was again 12 : 3 : 1, as in similar 



