Vol. 6, 1920 
GENETICS: C. W. METZ 
421 
> 100 and < 167 with the exceptions noted above are all regular and 
the last theorem is proved for these exponents p. 
I Gottingen Nachrichten, 1910 (507-16). 
^ These Proceedings, 6, 1920 (266). 
3 Trans. Amer. Math. Soc, 4, 1903 (201-12). 
Hilbert, Die Theorie der Algehraischen Zahlkdrpers, p. 430' 
s Hilbert, /. c, p. 429. 
« Crelle, III, 1893 (26-30). 
Ibid., 140, 1911 (29). 
« L. c, pp. 482-88. 
^ Ahhandlungen Berlin Academy, 1857, p. 73, verification of 2nd assumption. 
10 Kummer, /. c, pp. 63-5. 
II Crelle, 40 (93-139). 
^2 Berlin Monatsberichte, 1874. 
13 Hilbert, /. c, pp. 429, 435. 
OBSERVATIONS ON THE STERILITY OF MUTANT HYBRIDS 
IN DROSOPHILA VIRILIS 
By C. W. Mktz 
Station for Experimkntaiv Evoi^ution, Carnegie Institution op Washington 
Communicated by C. B. Davenport, May 28, 1920 
In an earlier paper^ by Metz and Bridges, attention was called to two 
cases of apparent incompatibility between mutant races in Drosophila. 
One of these cases involved my data on the sex linked characters rugose 
and glazed in Drosophila virilis. Subsequent to the publication of this 
paper another character appeared in D. virilis that shows the same rela- 
tions to rugose and glazed that they do to one another. ^ A study of these 
three characters has brought out some interesting relationships and has 
apparently revealed an error in the previous publication that should be 
corrected. 
It may be recalled that hybrids between rugose and glazed were in- 
variably sterile, while supposedly pure stock of each mutant was fertile 
and hybrids of either with other mutant stocks were fertile; hence it was 
concluded that rugose and glazed were incompatible. It appears now 
that a mistake was probably made in the statement that pure stocks of 
both rugose and glazed have normal fertility. Apparently this should 
have applied only to rugose, for later work has shown that females 
homozygous for glazed are usually sterile and that pure cultures cannot be 
maintained — at least without great difficulty. Possibly this condition 
has arisen by the secondary appearance of sterility factors in the stock 
since the previous paper was written, but more probably the earlier stock 
was impure, at least part of the time — the impurity having been over- 
looked through confusion with rugose in which the homozygous females 
are somatically normal. Unfortunately no accurate records of stock 
