Voi,. 7, 1921 
GENETICS: LANCEFIELD AND METZ 
225 
physical measurements and fields which up to the present time have not 
been covered satisfactorily by other means of investigation. 
The writer is greatly indebted to Dr. J. Gordon Wilson, Head of the 
Department of Otology Northwestern Medical School, with whom this 
co-operative research has been done and to whom equal credit for the 
success of the work is due. The writer is also indebted to Professors 
Millikan and Lunn of the Department of Physics of the University of 
Chicago for their helpful suggestions and enthusiastic interest during all 
the stages of development up to the present time. 
1 John P. Minton and J. Gordon Wilson, "Sensitivity of Normal and Defective 
Ears for Tones of Various Frequencies," Proc. Inst, of Medicine, Chicago, 1921. 
2 John P. Minton, "Physical Characteristics of the Bar," in preparation for the 
Physical Review. 
NON-DISJUNCTION AND THE CHROMOSOME RELATIONSHIPS 
OF DROSOPHILA WILLISTONI 
By Rebecca C. LancefiEld and Charts W. Metz 
Station for Experimental Evolution, Cold Spring Harbor, N. Y. 
Communicated by C. B. Davenport, May 5, 1921 
Of the eleven types of chromosome groups found in the genus Droso- 
phila (Metz '16) 7 that designated type A is the most widespread — occur- 
ring in 13 of the 29 species that were studied. This type is represented in 
figure 1. It consists of one pair of rod-like chromosomes, two pairs of 
long, V-shaped chromosomes and (usually) one pair of very small spheri- 
cal "m" chromosomes. 1 The constancy of this type among the 13 species 
is such as to suggest a genetic homology of the respective pairs of chromo- 
somes throughout. On the other hand the species themselves are scattered 
more or less at random through the genus and do not constitute a re- 
stricted taxonomic group. This suggested the desirability of a compari- 
son of the genetic constitution of the chromosomes in two or more of 
these species. 
Since D. melanogaster was already well known genetically and cyto- 
logically, and thus afforded a convenient basis of comparison, we under- 
took a study of D. willistoni, 2 a species resembling melanogaster in ap- 
pearan e and in chromosome constitution. In the course of this study 
we have found, by an examination of non-disjunctional flies, that the 
chromosomal resemblance between willistoni and melanogaster is mis- 
leading, for the sex chromosome pair of willistoni does not correspond 
morphologically to that of melanogaster but corresponds, rather, to one 
of the autosome pairs of this species. This would indicate that corre- 
sponding chromosomes in the two species are not all strictly homologous. 
The evidence for this conclusion together with a brief discussion is given 
below. 
