GENETICS: STURTEVANT, BRIDGES, AND MORGAN 
171 
flies each. Such meager data are clearly insufficient to establish accurate 
crossover values. But the values given by Morgan and Bridges are them- 
selves incorrect, as is shown by their account of the actual experiment (p. 68). 
The total number of flies is 69, not 59, and the crossover values accordingly 
become 17.4 for white depressed (instead of 20.3) and 14.5 for depressed ver- 
milion (instead of 17.0). The sum of these values, 31.9, is not significantly 
different from 30.5, the accepted value for white vermilion. This relation, 
and the fact that the 69 flies included no double crossover, give no warrant 
for supposing that the locus of depressed is outside of the plane that includes 
white, vermflion, and bar. 
Only two crossover values are given for shifted — shifted vermilion and 
shifted bar. It is evidently impossible to place a point in space by means of 
its distances from only two other points. Three are necessary, as Castle 
himself points out in connection with abnormal and bifid. There is thus no 
reason whatever for placing shifted out of the common plane. 
The aberrant position of lethal 3 in Castle's model is evidently due in large 
part to the fact, shown by Morgan and Bridges (p. 75), that the experiments 
involving this locus gave a value of 2.3 for vermilion miniature, which is less 
than the mean value, 3.1, used by Castle. The values obtained in the lethal 
3 experiments were: 
Lethal 3 vermilion 6.8 
Vermilion miniature , 2.3 
Lethal 3 miniature 9.3 
The third value is substantially the same as the sum of the first two — hence 
the three loci must be represented as lying very nearly in a straight line. 
In the case of furrowed, the values are all based on a few flies (240 or less 
in every case), and the three most important values (vermilion furrowed, 
miniature furrowed, and furrowed sable) were all obtained in different experi- 
ments, so that comparisons are hazardous. Furrowed is a character that is 
often difficult and sometimes impossible to classify, so that there is a large 
probability of error in the counts that have been reported. 
In the case of lethal sc there is only one available crossover value (bar 
lethal sc, 8.3) small enough so that double crossing over would be negligible; 
and there are no data involving lethal sc and more than one other locus at the 
same time. The data are therefore not of the type to give a decisive answer 
as to the relations of the locus. 
A careful examination of the data thus shows that a single plane suffices 
for the representation of the loci dealt with by Castle. Within this plane 
the positions of the remaining loci fall, in Castle's figure, roughly into a single 
curved line. The only noticeable exception is the locus of lemon. This locus 
is based on only 241 flies, and these gave rather too small a crossover value for 
the well established white vermiHon distance, so that this discrepancy is not 
significant. The arrangement of the genes is thus approximately linear, but 
